And like cars and trucks, I just seem to use whatever comes along.
I have a Husky Rancher 55 (bought for $75 that someone "returned" to Lowes. (18 / 20 Bar.
I have a Stihl 025 with a 16/18
I have an Echo arborist top handle saw (forget the model) with a 12/14 setup.
All 3 are great saws in my opinion.
My advice is to find an Echo dealer, my Echo dealer here is actually usually a buck or two cheaper than Home Depot, not to mention you get the saw running, full of gas, checked out and adjusted by a guy that does that all the time. The other reason I would tell you to get an Echo is the 5 year Homeowner Warranty they come with. I don't believe (could be wrong) that the other saws are anywhere in that hunt. I was looking at a chop saw last week and the Stihl came with a 90 day warranty (gag)
If you do not have a local dealer Baileys online is a great place to buy arborist stuff.
I also will second or third the helmet / chaps deal.
Oh, and another thing about the dealer, I asked my dealer about a case for my Echo when I bought it and he looked up on his shelf and grabbed me a used one for Free. I like Free.......
Good luck and be real safe, those chains don't care what they hit, and the guy I know that is the absolute best I have ever seen with a saw, is the same guy that cut through both bones in his leg with one while 70' up a tree. Has to be one of the most dangerous and useful tools out there.