If you're doing it right -- and in a way that can actually help you as a hitter -- you should use your bottom hand. I don't think hand dominance matters (I'm right handed. I usually hit infield righty, but I mostly bat lefty whenever I play softball/baseball).
If you do it this way, you can start pre-loaded. You don't really have time to load when tossing it to yourself in any meaningful way. For a lot of hitters who struggle to understand timing and load, pre-loading, tossing out in front (and not needing to do weird stuff with your hands to get them in position), and swinging can help.
I think bottom-hand tossers tend to exhibit more control, too, which is better for actually hitting infield/outfield.
I look like a moron if I don't use my glove hand. I may look like a moron whether I have a bat in hand or not, but still...