Like my wife says, focus on engine size rather than blade size.

Actually, that works well for chainsaws too because the larger engine will move the blade better. Keep the blade sharp, the air filter clean, and the bar oiled. But like others have said, it depends on what you're doing with it.
If you're just doing some limbing, then a 14-16" is probably fine. If it's trimming type stuff, then a 12" would be fine. If you're cutting up firewood, limbing, and occasionally knocking down a 24-30" wide hardwood tree, then a 16-18" blade is as big as you need for 95% of the homeowner type jobs. Ultimately though, I'd go for one with at least a 45 cc engine size if you're doing anything more than trimming.
I have an 18" Husqvarna 450 with a 50 cc engine and really like it. The only other saws I've used is a smaller Poulan Wild Thing and a professional lineman's Stihl. All ran fine. Even though it was smaller, the Stihl was a nice lightweight saw. But being a Stihl pro-series, it was also well out of my price range.