I’m a huge fan of 9mm carbines, but admittedly, I’m not terribly fond of AR9’s compared to dedicated carbine designs. The reintroduced Ruger PC9 has my full attention, especially with the PPSH-ish aesthetic of the Midwest Industries version. The other two common models have traditionally been the Hi-Point and the Kel-tec; the high point with poor aesthetic and barbaric quality, and the Kel-tec with only slightly more refined quality, but a relatively off-putting folding gimmick. The Beretta CX4 and HK USC are great entries in the class, if you like that space-age aesthetic, and I was personally excited by the Taurus entry a few years ago, as briefly as it lasted. The Sig Scorpion and MPX are probably my second favorite options in the current class, behind the Ruger - only because they’re in the AR9-ish realm a bit more than the others.
Personally, my money is being saved toward my SOT and an MP5 - I’ve been lusting over them for far too long. But until then, the Ruger does what I ask.