Recently I've been really looking into maximizing the value from my spending. I used to just have the AmEx Blue Cash Preferred card, which gives you cash back, but airline miles turned out to be much more valuable (to me at least), so I signed up for some more cards this year. FlyerTalk is a pretty good resource to check, but the format of the site (maybe intentionally) makes it difficult to quickly get up to speed on how to do things. I didn't end up taking much of the advice on that forum, but I still think it's a good source of information. One of the less cryptic and very often used sets of the abbreviations are from IATA airline codes.
Star Alliance is the largest group worldwide, so I tend to prioritize those airlines. The airline programs I'm a part of are for OZ, UA, SQ, and NH for the following reasons:
OZ (Asiana Club): It's comparatively easy to get Star Alliance Silver and Gold. I'm getting the Asiana BoA credit card, but disappointingly (but not surprisingly), the card points don't contribute toward status.
UA (Mileage Plus): Every flight you fly earns you points (whereas for some airlines cheap flights earn you nothing), though this is changing in 2015. I also signed up for this before I really understood what I was doing so I could get at least some mileage. They also seem to have decent rates for mileage redemptions and low taxes and fees. For a recent example, I paid $5.60 and 35K miles for a flight to Japan operated by ANA (which is right now my favorite airline).
SQ (KrisFlyer/PPS): I'm going to be living in Singapore for some time and the airline is apparently very nice.
NH (ANA Mileage Club): I love the airline and they have great search on award flight availability. Unfortunately it seems like you can't book one-way award flights, and you need a certain amount of miles in your account to search (I might be wrong on this last point, my Japanese is not very good).
For the cards I have, the Amex Platinum is decent and the Chase Sapphire Preferred is a bit better (it offers two 2x bonus categories).