Usually, bigger is better when it comes to target/range shooting, as the longer sight radius will help by minimizing the effect of small sight alignment errors. The difference between these two Glocks is not great, however, and if the slight difference in the frame "feel" of the G23 seems to fit your hand noticeably better, then you won't be seriously handicapped by the 1/2-inch shorter barrel and slide.
As there have been many G22s traded-in by law enforcement agencies over the years, you may find used G22 magazines far more common than used G23 mags; but if you're only buying new mags, then availability is about equal. In addition to its proper 13-shot mag, G23 can use the longer 15-shot G22 mags, they will just hang-out the bottom of the frame about an inch. The G22 can NOT use the shorter G23 mags, as they will not reach the magazine catch/release before the base stops the mag by hitting the bottom of the frame.
Honestly, it's a toss-up in most areas, and you could make the final choice based on looks alone and not be worried about ending up with a seriously "wrong" selection. If you were ever thinking of getting a carry permit, then I'd definitely go for the smaller/shorter G23, as it's noticeably easier to conceal in most clothing. But as a range-only gun, take your pick, neither one is a bad choice.