Which oil do you use?

I like to use 5W-30 in the Winter when it's pretty cold and pretty much 10W-30 (thicker) in the summer.
In a few past B2200 trucks that I had, I was told to use 15W-40 Rottella. A much thicker oil that would help decrease oil burning and possibly increase compression ever so slightly. I also used additives such as Bardhal (the thick syruppy stuff). I wouldn't recommend these for everyone though.
I haven't tried any Synthetic Blends cuz I'm not sure how much percentage synthetic they have? And I have not yet tried Full Synthetic since it is a more expensive oil and I figured I'd just stick with the regular oil, but do my changes more regularly.

sklein25 AT hotmail DOT com

Penzoil or Quaker state Full Synthetic 10w-30. some times I use that Zmax stuff, seems to work, my truck has 240,000 and does not smoke or burn oil at all, compression is awesome and even my mechanic friends did not believe me when I tell them my milage and that it was the Original motor and not rebuit.

Royal Purple Synthetic 10-30W in my truck.. Amsoil in my MX-3.

Tunes67

10-30 co-op dino oil. synthetics and their increased duration between changes is convenient, but i like getting underneath more often and taking a look at the rest of the underpinnings to see if I can catch a problem in the early stages.

Castrol 10W-40 High Mileage

Quaker State 10W-40 High Mileage