People tend to suggest what they like, reflective of their own situations, predilections and experience, which may or may not have any bearing on your bike commuting. Which is why 10 Wheels advice is solid - not just the test ride but you'll be talking with the (hopefully) experienced people there and narrowing down your choices.

The only general advice I could give at this point is to select the kind of bike that you'll like to ride, that you will ride. A commute is just a bike ride and all of the refinements that we like are really secondary. I suggest approaching it from that angle.