Type of work
Think about the type of jobs you'll want to tackle with your new power tool. If you just want something versatile you can use for a host of odd jobs around the house, a drill driver should be more than enough to get the job done most of the time.
However, if you want to drill into masonry you'll need to consider a hammer drill, and if you're looking to tackle specialist or heavy-duty tasks you may need to look into one of the other types of drills and wrenches available.