Solrus,
I have an "old school" DeVilbiss JGA-502, which is a suction feed gun, and a Devilbiss gravity feed HVLP gun. Personally, I don't like gravity feed guns because of the balance of the gun. I much prefer the balance of a suction feed gun...my opinion only. An HVLP gun will have a higher transfer efficiency than a non-HVLP gun (meaning more paint gets applied with less waste). The non-HVLP will require more air pressure.
I realize your question was about equipment, and not paint, but I'm going to throw this out as well. Paint comes in many forms and at different price points. Some colors are more expensive than others, with red being among the most expensive. Again...my opinion only, but painting a machine, and doing a thorough job, is a lot of work. Higher quality paints last longer...and they are more expensive. If you cheap-out on the paint it will not last as long, and you'll be doing it again sooner. What's your time worth? My recommendation is to use higher quality paints.
I had my first Tucker painted by a recommended shop. The cost was $1,500 and they used a catalyzed industrial enamel. It looked okay, but not great when I picked it up, and I sold it a few months later. I had a second Tucker painted by another shop for a little more money and they used that same catalyzed industrial enamel. This painter did a much nicer job, and the machine looked really nice when I got it. But it wasn't long at all before the paint started to fade. In my not-so-humble opinion, buying cheap paint is a false economy.
Here's the second machine after returning from the paint shop and being reassembled.