With the revised OP and a stated desire to fly between the Bay Area and NYC, your answer is United.

I'd recommend that anyone get the SPG Amex - it's the best primary-spend card out there IMHO. (Other cards have unique threshold bonuses that may be worth pursuing, but no other card that I'm aware of delivers points that are still reliably worth 4-5 cents each on modest Cash & Points awards.) However, it's not a good avenue to United miles. 1 SPG would convert to 0.625 United. You'd be better off getting one of new UA credit cards that awards 1 to 1.5 miles per dollar, depending on the level you get.

HH Amex is also a worthwhile card to hold...especially if you decide to roll most of your stays over to Starwood and use the HH CC as your backdoor to Diamond. (An example of one of those threshold perks that *might* be worth your while, depending on how much you value Diamond.)