In alll seriousness, for a rule of thumb, I recall an old marine saying. Dont show up to a gunfight with anything that doesnt start with a 4. That means, at least 40cal, 44 or 45, for practicality.
Then you need to think about capacity, fit, concealability (if your going to coceal it) or how your going to carry it. Every hand seems different and I know I shoot some of my handguns much better than others.
So, it all goes back to what the Weasel said, (I love that name
). Ask and you will get many answers.
For me, a good 45ACP that fits me and is fairly concealable with at least 10 capacity is hard to beat.