I personally would advice the following:
- Sports hybrid/trekking with a slightly bent over position but nowhere near racing position like on a road/CX bike; This will make it easier to keep your eyes on the road, ahead of you instead of on the road right in front of you. I often have the tendcy to look down when on a race bike or at least it takes more effort to look ahead of me.
- Make sure it has a fixed fork. for commuting you really don't need a suspension fork. A good steel/aluminum rigid fork is all you need. It will have much better steering and they usually can't break unless you collide with something.
- A rear rack is a bless. Then you can add a small pannier to carry your stuff you need, also a good place to store a rain jacket/ trousers, spare tyre and other stuff
- Bottle cages, make sure you have at least one, a good bottle cage and a good bottle are indispensable on longer rides. dehydration is the nr 1 cause of early fatigue.
- Check for eyelets to install fenders. You stay clean and dry with good fenders
Oh, and most important of all, make sure you can testride the bike to make sure it really fits you and is comfortable.