I use 5w-50 synthetic in the summer & 0w-30 synthetic in the winter. People who say once synthetic is used you can't go back to normal oil are full of shit. You can switch to synthetic, syn. blend, or conventional oil any time you want(wait til 3K new engines). The only time you should stick with full synthetic is when the cars comes from the factory pre-filled with syn(corvette, viper, BMW, Porsche, etc.) I change mine every 3K or 3months no matter what, people say you can go 7500 or more w/ syn. You know what I say, go ahead. Like the new BMW's, every 15K
, my buddies 330i starting ticking like hell @ 10K.
As far as brands go, all the major ones are fine. Mobil 1 Penzoil Amsoil Castrol Quaker State Valvoline etc.
Dyno test: Mobil 1 10w-30 syn VS. conventional 10w-30
http://www.importreview.com/reviews/...0-130valv.html