All good choices IMO, I have a 550xp and MS261. Air filter is better on 261, option for factory double spike/roller catcher is only availible with 261, inboard clutch on 261. The 550 just needs a pull of the cord to restart after shut down where the stihl you need to set the master control first. 550xp is smaller and a bit better balanced. Spool up is faster with revboost 550xp. Finish is better with stihl, captive nuts are better/heavier duty on stihl. Torque is slightly better on stihl. If l had to let one go I'd cry but eventially let the ms261 go before the 550xp. 5 series huskies are class leaders withe exception of the 576xp. But the new updated black clutch cover ms261 is lighter with more power but I have no experience with it yet.