I carry a fullsize Sig, and it conceals fine for the winter time. Look into getting a good holster, i use a CrossBreed. What ever gun you end up getting make sure it's one you can shoot straight and depend on. After all, your life can depend on it one day.
Also, if you're looking for SHTF gun, it helps that Glock makes 33 round mags that would fit in any 9mm Glock model. Wouldn't hurt keeping one or two of those around as a back up.
It's tough to say, if you carry a Glock everyday then I would go with the G34. Going from one Glock to the other won't be much of a difference ergonomics wise. Your hand will remember it faster. I say go with the one you shoot more. my personal preference would be the Glock.
I highly recommend the VP9. Great ergonomics and a very good shooter. Not a big fan of the striker ready indicator, looks kinda cheap, that's just my opinion.