It's not really a steel vs. aluminum thing... it's the way the tubes are made, put together, the bike geometry, etc.

My first commuter was a Kona Dew Deluxe. It served me well until I started riding 50+ miles more frequently and then it became quite uncomfortable. Personally, I'd rather have the steel Jamis Coda but I've gotten to a point where all of my bikes are now steel save that Kona I mentioned which is now just a back up for friends and sometimes a winter bike. That said, Marin makes good bikes. I owned one for a couple of months before dumping it because I wanted a different style. My best friend had one for years until it was stolen.