You can find lots of information on the topic of engine oil by doing a search of past forum discussions.
Driving in Canada, with the wide variance in temperatures between summer and winter seasons, presents a few challenges to selecting the best motor oil. 5W-30 is the standard recommendation for year-round use in our climate, but I always change to 10W-40 for the summer here in Edmonton.
I'll throw my 2-cents worth in and say that Red Line, Amsoil, Mobil 1 are the best synthetics and synthetics are the best oil.
However, if you have an older engine that is a little loose, you can benefit from running diesel-spec engine oil, which contains signifcantly more detergents and additives than gas engine oil but has the same lubrication qualities. Follow this link for a better explanation:
Just hoping to add to the confusion...
[This message has been edited by Dean Albrecht (edited 08-01-2000).]