It is as effective as the larger common self defense calibers but along with that it has a lower recoil (makes for faster follow up shots), is cheaper to buy (therefore you can practice more, and that is the real key, because shot placement is paramount), and holds more rounds.
I recommend a striker fired gun with no manual thumb safety. It’s just simpler, but I do recommend proper training and carrying it in a holster that covers the trigger guard area.
I like Glocks but there are a whole host of copycats that make good quality striker fired guns these days including but not limited to S&W, H&K, Springfield, FN, and many others.
Stay away from a revolver. They are not recoil friendly, they are slow to reload and they are not generally good guns for beginners.
A few of Glock models to check out, the G19, G26, G48, and the G43X.
If I was buying my first and only handgun, I’d probably get the G43X, but those are all good choices and there’s a huge element of personal preference.
If you are more concerned with home defense and not CCW, lean towards the G19 or maybe ever G17.
If you want something that can do both well, I think the G43X fits that bill.
If you know anyone who owns guns, see if they will take you shooting and let you try some different kinds.
I love doing that for new shooters.
"The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by an endless series of hobgoblins, most of them imaginary." - H.L. Mencken