+1 to CountGlockula.
It'll all vary depending on the use. Since it's a G23 I'm assuming concealed carry? Decide what material holster you want, either kydex or leather (no nylon).
Leather IWB:
- Milt Sparks VM2, Summer Special II
Leather OWB:
- Milt Sparks 60TK, MS 55BN
- Alessi CQC-S
Kydex IWB
- Comp-tac C.T.A.C
Kydex OWB
- Comp-tac beltslide, Blade tech beltslide KYDEX (none of that inj. mold. crap), side armor, or Ready Tactical.