I don't think the responders here are telling you to diversify exactly, they are telling you to explore your options. Usually the advice on FlyerTalk is almost the opposite of diversify, it is rather to consolidate stays/flights where possible and fiscally responsible, so as to achieve top tier status and maximize earned points and rewards. Research the programs with an eye towards which are represented well in your probable areas of travel. Pick a primary program. Pick a back up program. Stay with the primary when you can and secondary when you can't, but not to the point of silly loyalty in the face of major cost savings.

And as always: never stay in a hotel, fly on a plane, or rent a car without getting credit in the relevant loyalty program, even if it means signing up on the spot.

Some specific comments: I am a Starwood guy, love the properties and love the rewards program. They happen to be well represented in my travel areas, even internationally. But I am able to admit that for generic international travel Hilton and Marriott have way more options. Hilton has 3700 properties, Marriott 3150, while SPG has just under 1000. It can make a difference. I tend to think that the Starwood program has HH and MR beat hands down, but only where they are actually present. Hilton is my backup program, largely for my ability to get midtier status fairly easily.

Once you pick your primary program, you would be well advised to get the branded credit card(s) for that hotel. The SPG AmEx is one of the very well respected CCs around here, and provides great benefits and flexiblity. The HHonors Surpass card gives great point benefits when staying at Hilton properties, and there are several other Hilton branded cards that give lots of bonus points. Chase has a Marriott Visa with 70K points now. So whatever program you pick, get the cards to maximize the benefit, use them especially at their associated property for multi-point bonuses, and pay them off completely each month.

All good points. On this particular trip, I wanted to stay downtown to be within walking distance of places I mean to visit. So I booked the downtown Doubletree hotel with the Any Weekend, Anywhere rate for $149/night, which, admittedly, is not as cheap as the ones you mention, but a good compromise, I think.

I looking to get my first hotel credit card. My priority is converting the hotel points I earn to air miles. I use the air miles to earn free international first or business class seats. Is SPG the best program where I can earn points and then transfer them to AA, UA, DL, or even Southwest miles? Does it makes sense to convert hotel miles to air miles?

Only if you can't earn enough miles other ways and if you don't need them for hotels.

Hotel points, when used judiciously (ie, not in all circumstances) can be worth more as such than when transferred to airline miles. But if you find you never need hotel points (perhaps because you stay in other people's homes when traveling rather than in hotels, for example), then it may be reasonable to earn miles.

But have you already maxed out on airline credit cards? You don't tend to get huge points bonuses with hotel cards (once you factor in the hotel:airline conversion) the way you do with some airline cards (or even credit cards points cards that can transfer to airline miles in the case of UA). For example, the Amex SPG card only gets you 10K points (10K to 12K miles) "easy" and then only an addtional 15k points (for a total of 25k to 30k miles) with a high spend within a few months.

Compared to that, if you haven't yet (within the last 18 to 20 months), you can get 2 Citi AA cards (one personal Visa, one personal Amex) to 90k to 100k (depending on the exact offer), with no more spend needed total on 2 cards than on the 1 SPG Amex I think.

Then with UA, you can get a Freedom for 30k Ultimate Rewards points bonus, then a Sapphire Preferred for 50k UR points points plus that Sapphire Preferred makes it possible to transfer all your UR points to UA 1:1. And on top that you can also get a UA card itself, for another 40k or more bonus!

Compared to that, SPG is one-time 10k to 25k points bonus, and that's it. Ever. The one advantage of SPG, beyond the bonus, is that it has a 20% transfer bonus for transferring to AA and DL. But since it transfers to UA at a lousy rate (2 points for only 1 mile), I wouldn't recommend it for UA earning.

I don't understand why you want a hotel card instead of airline cards or Ultimate Rewards cards for ailrine miles. It's only the SPG Amex, no other, that gives you that 1.2 miles per dollar spent (in the long run); all other hotel cards give you less than 1 mile per dollar spent.

Club Carlson is not too back and getting a lot of promos. Easy to status match.

Wow, great information here. Thanks sdsearch for spelling it out clearly. I can usually find a good deal on a hotel room and will not get a hotel credit card. Since I've maxed out airline cards it looks like ultimate reward cards are the best answer for me.

While your post was generally sound, I feel compelled to point out two significant errors.

First, SPG is not a one-time bonus. The "first purchase" part -- currently 10K, as noted -- may or may not be a one-time bonus, depending on the length of time between applications. (I've gotten it more than once, and FT lore holds that a 2-year hiatus is enough to allow the churn.) That said, the "additional spend" bonus absolutely is not a once-off; you can earn it as many times as you sign up for the card, as I've confirmed in the past few years. (There's also typically a 5K or 10K referral bonus, which is a good option for tag-teaming by spouses/partners.)

Second, the SPG bonus for all airlines -- not just AA and DL, but also US & assorted others -- except UACO is 25% (for a 20K transfer), not 20%.

SPG is great for cash and points and reservation availability.
I'm not too keen on their properties vs something more luxurious like Priority Club.
For PC though, you are best to become an Ambassador and then you get upgraded easily. I am not a fan of their points system though, as it just is too much.

I have status at IHG, HH, Club Carlson, Best Western and Marriott. Marriott has the best properties, especially abroad. I like their mid-range hotels in Europe and Asia. I stay at hotels only for leisure so luxury is not my priority.

If you are going to spend some nights in Europe, then I think IHG or Marriott will be a good choice, if you are staying only in mid-range hotels IMO. IHG's priority club point breaks is awesome.

If you need to sign up for Marriott rewards, send me a PM and I can get you a referral and both you and I can earn up to 10K bonus.

The OP (of this question) only asked about AA, DL, and UA. So it was in that context that I mentioned only AA and DL as being potentially 1.2 miles per dollar.

UA (UACO for three more weeks) may be 25%, but that's on top of a horrible base net rate of 0.5 miles per dollar spent (because of the 2:1 base transfer ratio). The OP (of this question) was asking about the efficiency/wisdom of earning airline miles through a hotel credit card, and thus while a 25% bonus on transfers to UA may be true, it's basically irrelevant, because it still doesn't cure the 50% devaluation you start with (compared to not just the UA card but also Ultimate Rewards linked to either Sapphire Preferred or Ink Bold).

Meanwhile, while I realize that US is currently in *A with UA, and thus US miles can be used on UA, that may or may not be the case a couple years from new, depending on what happens with its attempt to merge with AA. (If such a merger did happen, it's much more likely that the combined entity would end up in OW than that two of the three remaining major legacies in the US both being in *A and none in OW.) That's why I never mentioned US as an alternative to UA, since the OP didn't ask about US.

Yes, but my point is that the ratio is 1.25, not 1.2.

Completely correct, and one of the many sound points in your first post on point. Transfering from SPG to UACO is a terrible deal and only to be done in extremis (e.g., to top off an account for an award that can't be redeemed any other way).

Back at the 10,000-foot view, I'll still defend the SPG Amex as the best all-around hotel card, and arguably the best loyalty credit card in general. It's definitely wrong for someone who wants to get UACO miles out of card spend, though.

Oh, sorry, I had misread your "except" as if it were saying only UACO was 25%. :)

So with UA, on top of the 2:1 there's also no bonus for a 20k transfer? (That is the other way I can read your post above, implying that for 20k with other airlines you get 1:1.25 but with UA you get 2:1 instead of 2:1.25.)