Look through the information at Superior (link in one of the posts above) I think that they have the best information.
My understanding is that a lot of quilters have gone to the Top Stitch needle as it has a little larger eye - read that "since it is larger it will be easier to thread". The needle size isn't any different between a regular needle and a top stitch - just the eye. That being said the other big difference in needles is the type: Sharp/Quilting/Top Stitch and Jeans needles are all "sharps", Ball Point are for knits and Universals are a combination of ballpoint/sharp. In piecing and free motion quiltiing I prefer a "sharp"