How much mental effort I put into my commute depends more on my route than which bike I ride. I used to have a nice route through some city parks, and in those parts, I could relax and get lost in my thoughts because I had very little to worry about in my surroundings. That route is temporarily impractical due to construction blocking easy access, so I'm on the roads more now, and I'm much more focused on my environment (i.e., traffic).