Wow, thank you to everyone for such helpful responses. It seems like AA is the way to go - especially with being able to snag 50k or 75k miles by signing up for one of their cards.
A related question:
Besides from getting more points from the AA-specific card, are there other advantages to choosing that versus an SPG card? Does it get access to clubs or other perks? And on the flip side, I'd imagine that benefits of the SPG card mean I can use points for plenty of other partners as well?