I struggled with the same decision when I bought my G23. I chose the Gen 4 because the slightly smaller grip is a better fit for me. I also really like the grip texture of the Gen 4, but in all fairness I can see why some may not like it. It is rough.
My Gen 4 G23 has been flawless. However, the round count on it is very low, less than 1,000 rounds. It flings brass into the next zip code if using properly loaded ammo. Mild ammo still ejects well, it just doesn't fly as far. My RSA is the 0-3, which is pre-replacement.
I say go with the Gen 4 if your hands are smaller like mine or so large that the Gen 3 grip is too small. If not, either will work well.