Right now I have Amsoil in my '98 Caravan and Mobil1 in '89 S10 Blazer since new which has 194K mi. The engine still seems very tight. Most people I know that have commerical vehicles are using synthetic. There is a good article at www.vtr.org/maintain/oil-overview.html Check it out!
I attempted to change my oil last Feb. I got it drained, but couldn't get the damned filter off, so I had to take the ****er to Quik Lube. I had to put my expensive Valvoline Synthetic Oil in to get it there. They drained out about a quart when the changed the filter, and added standard 10w30. So I actually have a mix. In about 2-3 weeks when it starts warming up around here, I'm gonna take it back (they only want 15$ for an oil change, and thats as much as it costs me in oil and a filter, and they do use good oil) and get a heavier weight oil put in for summer.
Dude, go with Mobil 1, I brought both my pickup and my wifes avenger to get the oil changed to MY mechanic and he told me, "I dont want to take your money, do it yourself with Mobil 1" He also told me he opened up an engine with over 100,000 miles on it and couldnt tell the difference with one with 10,000 on it (it had synthetic oil the life of the engine). Anyway just my opinion.......
I'm still breaking in my re-built engine on Mobil conventional oil. then I will go back to using Amsoil 10-30 . I love the fact that it comes in gallon containers. also have it in my diffs. hope to put it in my trani soon too, but thats a bit of work and messy.