I've owned Stihl, Husky, Poulan, and Echo. I'll go Stihl from now on. To me the difference is ease of start. The Stihl's I have owned have always started on one or two cranks. Over the years I've had o17, o19, o23, o24, o25, o26, 029. All good saws. Currently have O17 or MS170 not sure which, but they are the same. O25 with 16" bar and chain. O29 with 20" bar and chain. The only thing I don't like about the 17 is the size of the chain. It is a smaller chain and does not last as long. Really too light to do much work. I keep it around strictly for limbing. The O25 is my favorite choice. Really big enough to do about anything and the chain is of working size. I disagree that the O29 has enough power for running a 20" bar and chain. I keep it strictly for felling. It is underpowered with the 20". I can't imagine you needing it, but they are excellent saws just a little heavy. Stihl has their line of pro saws. For the homeowner thay are overpriced, only because you don't need them. I would say anything from O25 up unless you don't care about the length of time the chain will last. In that case 17 or 19 would do you fine. Just stay away from the easy tightening systems they are putting on the new saws. Mechanics at the local shop say they don't last.