Since your thread is asking for the 'opinion' of others. I shouldn't feel like a jackass expressing my own opinion on the matter.

If I could have only one bike, for commuting, the only bike I had.-----It would be some thing with a freewheel.

I have/ride/enjoy a track bike/fixie. A big plus is how simple the drive train it.

But having 6 complete bicycles working/together. I always just take what ever im 'feeling."

I don't know your situation, but you should have two bikes if your commuting, because some times when you walk out to your bike to leave for work you'll have a flat tire or some thing. Go to a thrift store and get a back up for 10 dollars.

My favorite commuting bike is my Trek 520