If you read up on arborist or logging sites, you'll find that there are four brands that get recommended, and two that are most heartily recommended: Husqvarna, Stihl, Jonesred, and Husky. Husqvarna and Stihl get the most recommendations, probably due to dealer representation. From neutral parties, I've heard it said that you can't go wrong with either the Husqvarna or Stihl, and that you're better off just buying the one with the closest dealership that will service you well.
I've used the comparable Husqvarna and Stihl consumer models with the 16" bar, and felt that the Husqvarna was not significantly, but appreciably, stronger and faster cutting, so I replaced my 18" Poulan with the Husqvarna when I found it on sale at Tractor Supply. A 3 year no questions asked replacement warranty cost me $30. I also picked up the 20" 455 Husqvarna Rancher to cut up the 33" maple trunks from this spring's carnage. The extra power from a bigger saw and longer bar make a huge difference. While you can cut a 30" trunk with a 16" bar, it took me close to 25 minutes. With the 455, it took less than 5 minutes.