I cut about 10 cords of firewood per year and I do it with a Stihl MS-361 with a 24" bar. It's big enough to get through the biggest hickory logs without any problem at all. I also use it for trimming branches, but if I had the $$$ I would get a lighter 16" saw.

People swear by certain brands, but I think how long a chain saw lasts has everything to do with how well you maintain it.