Absolutely stick with one of the 'pro' models if you can afford it. If not then a MS280 would be a good choice. For an 18-inch bar you would want around a 60-cc motor. The MS290 is Stihl's best selling saw, but it is also the least expensive 50-cc saw they sell which is why. You pay for that low cost with the worst power to weight ratio in their line.
Scag Tiger Cat 48-inch deck, Kawasaki motor
Lawnboy 10227 2T push mower
Stihl BG86 handheld blower
Stihl BR550 backpack blower
Stihl KM110R kombi system with lots of attachments
Stihl HS45 hedge trimmer 24-inch blades
Echo SRM210 trimmer