I suppose it depends on what you want to do with it. I have an M11/9 and a Group Uzi. I used to have a MAC10/45 with a 9mm conversion. I ran a TASK slow fire conversion before Lage started building slow fire uppers. The only change I've Uzi was to have BWE add a feed ramp so it would run ammo other than round nose.
While it's true there are more options & accessories for the MAC series, it's because they need them to become "like an Uzi". My Uzi cost about what a tricked out M11 goes for today. My M11 cost slightly less than what I paid for one of my Lage uppers.
I really like my Uzi, but if I was shopping for one today, I'd get an M11/9. It's not a military gun, and it's not as robust. But it doesn't need to be, for a recreational shooter. It does everything I need it to at half the price. The Uzi can do .45 ACP which the M11 can't. Again, it depends on what you want out of it. I have 5 different caliber conversions for the Uzi but I rarely shoot it I anything other than 9mm.
One thing, the Uzi suppresses very well with no gas blowback issues. The MAC 10 seems a little noisier, but again no blowback. The M11/9 suppressed blows all sorts of gas back into the shooter's face. Gas blocks can help quite a bit, but it's something to be aware of.
As noted, I the $14K price range, you can get an FNC or an AC556. At that point you're pretty close to an AR15 conversion. I nearly bought a converted AR on a couple of occasions, but never quite got there. Again, I'd probably convert it to 9mm and shoot that 95% of the time. But that's me.
Good luck with your decision.