Personally, I don't understand the whole "9mm Carbine" fascination...
Don't get me wrong. I *LIKE* 9mm Carbines, especially the Colt 9mm I fired last weekend!
I've fired Beretta Storm 9mm's, Kel-Tec 9mm's, and an Olympic Arms 9mm...
My general opinion on the issue is this:
1.) What would you "USE" a 9mm Carbine for? I can only think of -Home/Self Defense, -Target Shooting, -Plinking, -Carbine Training... (You may be able to shoot small game [note: I didn't say, 'Hunt'], but it's not really what I'd call a "HUNTING" cartridge.
2.) The compact-ness of the 9mm Carbine (especially that of the Kel-Tec) gives it a specific niche of "Car Gun" or "Backpack Gun" that it can fill.
That said, I think the COLT, BERETTA, and KelTec are the best options. The Olyarms jammed a *LOT* (not bashing Oly, my 1st Ar was an Oly). They can all do the same (generally speaking) job almost as good as one another. It's just a matter of what you want to do the job, and how much you're willing to pay.
If you want the *BEST*, IMHO, buy the Colt, but you'll '$pay$' for it. If you want good accuracy & reliability, for a moderate price, buy the Beretta. If you want decent (but not that great) accuracy out to ~100 or ~150yds, buy the KelTec.
If compactness is important, buy the Colt or the KelTec (For break-down size). If not, buy the Beretta.
I'm not rich, so I'll someday probably buy a KelTec (and I like their Cust Service). In the meantime, I'm keeping all my ARs in 223, and maybe someday I'll buy a 300 Whisper.
That's just my opinion, and it's worth only what you paid for it (nothing).
-iNuhBaD