Stay the hell out of the big box stores and buy from someone who stocks parts and makes repairs, your saw will be properly set up and the money tends to stay in town.
You don't need anything bigger than a 16" bar, the high revving engines now 13,000 rpm cut very well and a bigger saw is just bigger aches and pains at the end of the day.
The midrange of saws would be the ms290 aka farm boss by Stihl but it's a lot heavier than what you need.