If you are just beginning, it will be a while until you are an elite.

Even 4 trips SFO-Europe return may not be enough to get you significant elite status if you buy the cheap fares....I am sure I will be shot down on this one....but I only said MAY :-)

I would maybe look at which would get you the best upgrades using your collected miles and which offer award travel within your region at the best conversion rate.

If you want to use miles from Germany, then LH or SAS are probably good, and you will get status in *A and thus United, which offers cheap flights within the US.

If you want to use award travel within the US, then United may be the best bet.

AA is still pretty good, and with the Platimum Challenge (search AA forum) you should get status pretty quickly, and thus increase upgrades. However, AA program is going through some serious changes, so you wont be able to use miles for upgrades unless you pay $250 each way.