Well as a fairly new handgun shooter I'll give you my 2 cents - probably worth at least 1 cent
I went to my local range and rented several guns before I bought one. I tried a Glock 17 & 19 (9mm) and a Glock 23 (.40cal). I found I shot the 23 no worse than the 19, but liked the feel of the larger 17 better. Based on that I ended up buying a G22 gen4 (.40 cal). I quickly found that I made the right choice as you can actually find .40 cal ammo while 9mm is hard to find and what is around is going for more money than the .40 cal. Since this gun is for range use and HD I was not concerned with small size, as a normal person cannot get a carry permit in NJ. Also for HD I liked the greater power of the .40 cal, figured if they are good enough for cops they are good enough for me. I will be getting a Kimber Eclipse Custom II (.45 acp) shortly. I was amazed at how well I shot that, and the perceived recoil (because of the mass of the gun) is much less than the .40 and even the 9mm in my view. But I will still use the G22 for HD as you can't beat the reliability of the Glock. I have 600 rounds through it so far and it has not had a single failure of any sort.
Oh one other thing, I don't see the capacity as an issue as I live in the People's republic of NJ where the max magazine size is 15 and that may be on its way to 10. My G22 .40 cal holds 15 rounds.