There are many people that will give you differing opinions on chainsaws, it's almost as bad as some of the gun debates.
Some will say "Only buy the $600 Stihl, the rest are junk."
Personally I have a 20" Poulan Pro, which I have used the crap out of and it's still going strong. I've had a couple of Poulans over time, and never had any problems with them.
I lot will depend on what you're going to use it for. If you're clearing storm debris then anything might work. If you're cutting up 36" oaks professionally, then you're going to want a better saw.
You might also want to checkout this site:
http://www.arboristsite.com/chainsaw/