Sapphire. United's not going away, but Continental is. You can transfer Sapphire points, all 50K if you want, into Continental for merger later into United's program. There are also transfer options to BA and a number of hotel programs. United will continue to offer some sort of card after Continental goes away, and I wouldn't be surprised to see a large mileage bonus offer after the merger is complete.

That's entirely my speculation, but it seems that United/Chase is laying awfully low with bonus offers to the general public at 25K to 30K at a time when American/Citi's running 75K to 100K, Amex is running 50K to 100K, and BA/Chase just closed out a 100K and is now offering only (?) 50K. A 25K to 30K offer doesn't feel like a worthwhile offer in the current climate, but I could see United/Chase holding back until the right moment after the merger is complete and then making a 50K to 100K offer. And I don't see anything on the horizon that would suggest that United/Chase is likely to pull back the current offers and put out a card offering a 10K to 20K bonus.

I wouldn't take the EQM bonus as much of a reason to devote a chunk of spending to these cards. If you're going to spend $5000 at United.com, the 5000 EQMs for the Mileage Plus Select are probably OK, but spending $375 for a Mileage Plus Club card, $35,000 for 5000 EQMs, and $50,000 more for 5000 more EQMs? If you're regularly, maybe exclusively flying United, it might be a good strategy, especially because the Club card includes an RCC membership, but if you're flying other airlines, I think you'd find better ways to spread $85,000 worth of spending amongst a lot of other cards offering mileage or point bonuses to meet their spending requirements.