Gonna depend on your definition of "best".
I have a Suomi that has a 70rd drum. Heavy as hell, though. But 70rd drums? Yeah, three drums and you could hold off the zombie apocalypse.
I have a Sterling carbine with 34rd mags. It's simple construction and a lot of fun to shoot.
You could argue a $200 Hi-Point and $800 worth of ammo would be the BEST carbine.
I'm guessing none of the 9mm carbines are any more accurate than the other. Come to think of it, I've never seen a comparison online. I like the Taurus carbine but the mag capacity hasn't been expanded. And the price is too high for what you get.