For me, ribeye. But I won't turn down a strip. It basically comes down to what's on sale when I decide to do steak unless I'm splurging on something nice (like hitting the prime rack at the butcher). For instance, t-bones were $5.99 last night, and they really were more like porterhouses (the filet portion was ginormous).
As for filet, they are very lean and very tender, but that comes at a cost. To be that lean and tender, they get very little work, which in the end means very little flavor on its own - one of the reasons why restaurant preparations almost always pair a filet with some kind of sauce.