That's a pretty broad question. What are you defending yourself against? What do you expect your attacker to be wearing? At what range do you expect to engage targets? Do you need to address the issue of over penetration of walls? Do you possibly need to shoot through glass or metal?
The list goes on from basic to ridiculous. I'd recommend getting Federal Premium Personal Defense in 165 or 180 gr, and alternate between them and FMJ in the magazine.
I have a glock 23 as well... Maybe you are having the same issue I have....
I find that 180 gr fmj is not very nice to shoot.
165 gr fmj is a decent shot.
180 gr hollow point is a decent shot.
I'm wanting to try 165 hollow point to see how that pans out.
IMO, you shoot what you can handle... I would not care if .40 180 gr fmj would blow a BG to bits... it would do me no good as I'm not sure I'd be very reliable with it past the first shot. Who am I fooling, I know I wouldn't. It would be stupid for me to carry that round.
180 HP is very decent for me... although, I'd like to get my g23 to the "smoothness" of my last 9mm glock, a 17. It won't take much, I'm thinking the 165 HP would do it... and yea, I've practiced... had the gun for a while (years) now.... practice at least once or twice a month.