First handgun Rule(s) of Thumb...
.22 lr., either revolver or semi. Reasons, lack of recoil, cheap ammunition means you practice more, some are VERY accurate (and that's always gratifying). e.g. Ruger MkII, Browning Buckmark, Ruger Single Six
Followed by... either a 9mm semi or .38/.357 revolver. Reasons, good first centerfire, power level can range from easy to pretty snappy, ammo weights & speeds from small to large, slow to fast. Ammunition prices range accordingly low to high. Some are VERY accurate. Some choices are good for self defense, either at home or carry. e.g. Ruger GP-100, S&W M10/64, 65/66, 36, 60,etc., Glock 17/19, Browning HiPower, S&W 39/59/69 series, Beretta 92, etc.
From there, it's your choice based on your wallet.
Go rent some at a local range. See what feels right in your hand. See what works for ya and what doesn't. Single action, DA/SA, SA Only or DA Only, blue or stainless, short barrel or longer, revolver or semi, fixed or adjustable sights... the combinations are endless.
Snub nose revolvers are, or should be considered, experts firearms, but will do in a pinch (all it takes is a few thousand rounds downrange and some serious dedication).
Have fun deciding.
My route went... Ruger MkII (.22), Dan Wesson 15-2 (.357, tho I shot mostly .38's in the beginning), Colt Gov't (.45 acp) Taurus 99 (Beretta 92 type) in 9mm, Ruger Bisley in .45Colt. But I knew I wanted a .22 first so both my wife and I would enjoy plinking together. It was the right choice... for me.
YMMV