I currently carry a G23 but just traded a Kimber for a G19C and FNP-9 as I haven't ever had a 9mm before. After shooting the G19C w/ the compensated barrel I found a kind person willing to give me a non-ported barrel and will re-evaluate after I get it but so far I must say I like the 9mm.
The sad part is I will have to get night sights and stock up on bullets and brass for it if I decide to carry it as well as SD ammo. With my G23 I got an aftermarket barrel as I didn't like the buldges left in the brass since I reload everything. I also have a G20 and a few thousand rounds for it that I can load up sometime. My only decision is whether to sell my 3K+ 10mm plated bullets and get 9mm bullets or keep them all and add 9mm bullets. If money wasn't a concern I know what I would do :)
In hind sight I wish I would have started out with the 9mm though and not bothered with the .40 S&W as it is all about shot placement anyway and I could shoot more if I shot 9mm instead.