Thank you draver for mentioning Roamless. For my travels, I typically use esims.io and/or esimdb.com to find country-specific or regional SIMs for the upcoming trip. Often that means buying packages of more GB than I need because it's hard to anticipate usage.

Roamless does offer that no expiry model which sounds great. I was also thinking about getting an eSIM for my Galaxy Watch 7 in the rare situations I will be without my phone (and not wanting to pay Verizon a monthly fee). A pay as you go usage model seems great for that.

However, as you mentioned some of their rates are not as good as others (I'm going to Mexico in Dec, my US Verizon plan will cover me on my phone, but if I use my watch, Roamless is quite pricey at $9.45/GB). This got me looking at some of their competitors (pay-as-you-go or global long validity), I figured I'll compile my findings here, incoming long post:

At the bottom is a table of some popular(-ish) travel countries in various regions. I came up with the table prior to looking at the different providers so that I won't be biased by their offerings.

Roamless (roamless.com):
The rates are different per country, as listed below.
181 destinations per their marketing.
As mentioned by draver , the rates can scale cheaper with some sign-up and top-up promotions.
No expiration - but you're loading dollars, not GB, so the price could go up on you.
Pretty good 5G coverage with some LTE per their website.

Unisim (unisim.net):
The rates are different per provider per country, cheapest listed below. This means you must manually select the provider per country to ensure you're getting the rate you expect.
Some providers within a country vary wildly (within Mexico: AT&T $8.70, Telcel $8.95, Movistar $16.15). Others vary less(France: Bouygues Telecom $1.58, Orange $1.76, SFR $2.16).
170+ countries per their marketing.
No expiration - but you're loading dollars, not GB, so the price could go up on you.
Does not show which networks are 5G vs LTE etc.

Yesim (Yesim.app):
Multiple options including local/regional/global plans.
They have a similar pay as you go model to Roamless and Unisim. Rates are in table, almost but not always more expensive than Roamless and Unisim.
They also have a Global 20 GB plan for 1 year for $64.90 ($3.25/GB) making it a little more than Staff Traveler.
They cover 173 countries in their PAYG plan. 147 countries in their global 1 yr plan. All the countries in the chart are covered by both plans.
Very good 5G coverage in their PAYG plan. Their global 1 yr plan is more of a mix of 5G and LTE (and a few 3G).

Staff Traveler eSIM (stafftraveler.com/esim):
One rate for all countries, don't have to think about high rate or low rate countries.
The bigger plan you buy, the cheaper per GB, so this really scales with usage unlike the ones above.
100 MB for $0.99 ($9.90/GB). 5 GB for $24 ($4.80/GB). 10 GB for $38 ($3.80/GB). 20 GB for $62 ($3.10/GB). 50 GB for $119 ($2.38/GB)
160+ countries per their marketing.
Importantly: 1 year expiration on the plan! A top up does NOT extend original plan. But you're paying for GB, not dollars.

ETravelSim (etravelsim.com):
They have a Global Flex 360 eSIM valid for 365 days. So if you're okay with the limited country list, it's cheaper than Staff Traveler as long as you have 10+ GB of usage.
10 GB is $30 ($3/GB), 25 GB is $60 ($2.4/GB), 50 GB is $110 ($2.2/GB).
Importantly, only 60+ countries per their marketing. Many missing on the table.

Firsty (firsty.app):
Different payment structure entirely, but still unique.
160+ countries per their marketing.
Free: Watch an ad, get 30-60 minutes of free SLOW data. Others have noted this is quite slow and most useful if you need to, for example, have data to activate another eSIM and don't have Wifi. Or just need to send out a message on WhatsApp.
Paid aka "Firsty Fast": No ads and is faster, comes in two options:
-Comfort Plus - 1 EUR/day ($1.08/day) = "High speed". No hotspot. Approx 700 MB/day until throttling
-First Class - 2.5 EUR/day ($2.70/day) = "Extra high speed". Hotspot allowed. Approx 2 GB/day until throttling
Some countries show a higher EUR/day instead of 1 EUR/day for the cheapest paid option, I listed this in the chart.

Nomad (getnomad.app):
A little bit closer to traditional but I included their global plans, because they often appears in these discussions and have long validity.
Their 10 GB plans are only available for 180 days so I'll skip pricing. Their 20-50 GB plans are valid for 1 year.
They have 2 global plans: 54 countries and 81 countries. The former is quite restrictive, especially in the Americas.
54 countries: 20 GB, 30 GB, or 50 GB are all priced at $2.50/GB ($50-125). This plan seems worse than ETravelSim.
81 countries: 20 GB or 50 GB are priced at $3.40/GB ($68-170). This plan seems worse than Staff Traveler.

Saily (saily.com):
They seem to have traditional time-limited plans. They also have globals with short validity.
But I'll list their one global plan with 365 day validity: $67 for 20 GB ($3.35/GB). So Staff Traveler seems better.
105 countries per their marketing.

BNESIM (bnesim.com):
Has non-expiring pay-as-you-go esims for only some regions, with various package sizes, such as:
Europe: 1GB $2.27, upto 20 GB $39.51(=$1.98/GB).
Asia: 1GB $4.43, upto 20 GB $77.14(=$3.86/GB).
But usage is for within that region and not shared to other regions!
The global plans as well as many other places don't have a pay as you go plan and are instead traditional style plans.
I did not include this in the chart for that reason. But included here because often discussed.

KeepGo (keepgo.com):
Not a universal plan. They have various packages that include either regional or more/less inclusive global packages. A bit pricey but including because often discussed.
All their plans expire after 1 year, unless you top up the plan which extends your plan for another year. For example, you could have a 50 GB plan with 30 GB remaining, if you top up the minimum (currently 100 MB for $3), you extend for a year.
Their current global ones are "Tucana" and "Eridanus", the former appears new:
Tucana - 85 countries. 1 GB $9, 5 GB $28 ($5.6/GB), 10 GB 45 ($4.5/GB), 25 GB $80 ($3.20), 50 GB ($3.10)
Eridanus - 100+ countries. 1 GB $21, 5 GB $70 ($14/GB), 10 GB $100 ($10/GB), 25 GB $220 ($8.8/GB), 50 GB $400 ($8/GB)
Currently they have a promo of buy 1+ GB, get 2 GB free - once per account. So 3 GB of Tucana costs you $9 ($3/GB) which is pretty good. 3 GB of Eridanus therefore costs you $21 ($7/GB) which is arguably worse than Staff Traveler except the ability to extend expiration.

Eskimo (eskimo.travel):
All of their plans are 2 year validity (and rollover for additional 2 years with every top-up, so you can keep rolling over indefinitely). Looks like minimum top-up is 1 GB.
Their Global plan is only 83 countries per their marketing. Indeed missing countries on the chart.
1 GB for $7. 3 GB for $18 ($6/GB). 5 GB for $25 ($5/GB). 10 GB for $39 ($3.90/GB). 30 GB for $90 ($3/GB).
So, pricing not far off from Staff Traveler. Downside is worse country coverage. Upside is longer validity (+ rollover).
All LTE coverage, no 5G.

DENT Wireless (dent-app.com):
Their global plan is $10 for 1 GB or $9/GB for 5-10 GB. 1 year expiry. So they're like a more expensive Staff Traveler, therefore I did not include their country list in the table.

Drimsim (drimsim.com):
Similar pay as you go model to roamless. But the prices were MUCH more expensive. Including because mentioned elsewhere but I don't see a reason to use them. Minimum of 10 EUR/GB for the cheapest countries. As high as 50-150 EUR/GB for some of the others I checked.

Airalo (airalo.com):
Their only global with long validity (1 year) is 20 GB for $69 ($3.45/GB). Making them still slightly more expensive than Staff Traveler if 20 GB is exactly what you need.
136 countries per their marketing. All countries in chart are present.
Mostly good 5G coverage with some LTE countries.

FlexiRoam (flexiroam.com):
They have various package plans. Their global with long validity (1 year) is similar to Airalo but more big data options (all more expensive than Staff Traveler).
20 GB is $69 ($3.45/GB). 30 GB is $99 ($3.30/GB). 50 GB is $149 ($2.98/GB). 70 GB is $199 ($2.84/GB).
130+ countries per marketing. All countries in the chart are covered.
Does not list 5G or LTE.

WorldSIM (worldsim.com):
Only PAYG they have is WorldSIM International eSIM Pro and the data rates are quite high so I didn't fill the chart.
Some examples: $5.90/GB US. $7/GB Italy. $13.40/GB Mexico. But this plan does also have ability for paid-per-minute calls.
Their non-PAYG data plans are short validity.

eSIMPlus (esimplus.me):
PAYG non-expiring global where you top up dollars not GB, like Roamless/Unisim/etc.
146 countries covered. Rates are quite high so I didn't fill the chart. The absolute cheapest rate is $6.80/GB, only in a few countries.
Some examples: US is $12.80/GB. Mexico $57.40/GB. Italy $11.40/GB.
No info on 5G vs LTE.

silent.link:
Very similar model to unisim, pay by network in country. But appears to only accept crypto for payment so I did not populate the list. If you are willing to pay with crypto, take a look at them. Pricing seemed to beat both unisim and roamless.

Red Bull Mobile (esim.redbullmobile.com):
Appeared to be similar to Roamless. However, outside of the trial plan, you buy 1+ GB per country with 31 day validity. Confirmed by their customer service.

I couldn't put the table directly, so here's a screenshot:




10/29: Added Yesim, Eskimo, Airalo, WorldSIM, eSIMPlus, FlexiRoam info. Added some info about 5G.
10/30: Removed Redbull Mobile from chart.