Well, having grown up with a Stevens single .410, I'd have to say that the "semi-hammerless" 37 has advantages. But the 220--and Savage was a pretty good name back in the day as well--avoids the issue of a hammer that can be hard to cock as a bird flushes. If you have time--I learned hunting squirrels, as most of us did back then--cocking the hammer is no big deal. But there can be a lot of hammer fumbling when a bird surprises you with a flush.
The one advantage with the hammer: Allows you to see immediately that the gun is not "on safe". But the 220, with a tang safety, makes for a very smooth transition to a double.