I used Mobil1 for a while before I rebuilt my engine, was always happy with it. When I tore down the engine, everything was decently clean (surfaces were stained, but no sludge, grime, or any kind build up), even though it had been pretty badly abused before I got my hands on it. I'd recommend Mobil 1 to anyone, and I still use it in some of my family's cars.
Now that mine is freshly rebuilt and broken in, I'm trying the new Pennzoil PurePlus stuff. I've heard good things about it, and so far I like it. I'm keeping track of my MPGs (or MsPG) to see if it actually improves gas mileage like I've heard. Seems like it does a bit, but it's still too early to say for sure.