The OP may end up liking both, or preferring one over the other. The recommendation to try both at a rental range is a very good idea.

Having said that, you can hardly go wrong with a "compact" (not small) or full size pistol, like the various versions of the M&P-9. And 9mm is a good caliber to start out with. You can branch out later.

If you decide to go with a revolver, a mid-sized revolver (something like a S&W K Frame) is a good thing to start with (not a 642). The 642 is a pocket revolver, and very good for what it is -- but not a fun gun to shoot at the range, and smaller than it needs to be for home defense.

Anyway, give a few guns a try at the range, and if you get one type or the other, there is no reason you can't branch out later. I'd bet most folks on this revolver forum also have pistols!

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S&W Rover