HVLP guns have a lot more air holes in the atomizer- you can really see the differance if you hold them side by side.
The nice thing about the newer guns is they don't waste as much paint. As long as you spend some time doing some setup the finish comes out nice.
As far as tip size goes, you need one that is big enough to lay down paint fast enough that you can maintain a wet edge on the job you are doing, but not so big that all the paint comes out of the cup in one shot.
