Unless you know how to work on a chainsaw, or want to learn how, buy a saw from a local saw shop who can service it for you. Stihl, Husky, Echo, Dolmar - they are all good and will run for years if used properly and serviced regularly. If you value weight, or lack of it I should say, then buy a pro quality saw. With Stihl, that's the white handled ones, with Husky the XP's (unless they've changed). They are easier to work on, too, when needed, which will be less often. In my opinion, the Stihl MS 361 and Husky 371XP (or whatever the new models are) are about the two best all round saws made, light enough to use all day, big enough to take down anything up to 24" or so.
John