Price Point: I'll start out with calculating your past years spend and which US hubs you fly to the most. Based on the spend, see which US program will meet your needs financially, such as Delta Diamond (28,000 USD).

Perks: Most US based flyers will value the US3 FFP due to free choice of economy plus equivalent seats at time of booking and also domestic upgrades (becoming much harder now, since airlines will sell seats on the day of the flight rather than giving it to FFP members). Domestic US lounge access rules are also important, Delta is getting stingy on domestic lounge access compared to before. As for GUF/Joker equivalent, unfortunately, the US3 certs aren't as easy to use for immediate upgrades now a days due to inventory restrictions, and you'll have to be flexible or willing to chance it. Delta does one class upgrades now, but Global Upgrades can be used with select AF/KLM flights also.

As for Avios equivalent redemptions, Delta is probably the worse in terms of number of miles needed. AA still has really good OW partner redemptions in J/F; albeit much harder to find now.

As for invite tiers, I can speak for AA and UA, that you don't need a CC to be invited. US3 programs look at how valuable you are as a customer to them, so most are looking at 50k+ minimum in spend in J/F cabin; and most will require multi year spend history.

If you know if you have a set spend pattern and capital upfront and want an invite tier status, UA PassPlus program will get you automatic GS at 75,000 up front balance deposit.

As for Delta specifically, they opened a new Delta One lounge in JFK and LAX; and they are much better than any other US3 lounges at the current time. Their app and websites works very well

Delta has better customer service compared to UA/AA.