I mostly stay away from the M4 platform too. Just a personal preference.
I have, among other things, a Krytac Vector and I love it.
Pros:
Looks different
Fun to shoot
Very customisable
For the past 3 years it has been VERY reliable
Maneuverable in confined situations
Cons:
Mag sizes. 120 round mags, or smaller, or a drum
Mag pouches. Finding pouches for a Vector mag can be a pain. I've gone kydex, from Deadly customs as their kydex SMG holsters take Vector and KQA smg mags (I also have a KWA QRF MOD2)
Upgrading: I have never opened mine up, I run it stock, but I hear people hate working on them as they are so different to other RIFs internally (Luke Neg Air won't even touch them)
Weight. For a "CQB SMG" it's pretty heavy. Not awkward and cumbersome, but it's not as light as it looks.
Overall I really enjoy my vector, and it is a head turner of a gun.
Can't speak to the AUG, never used or owned one.
Vector in action.
Also: Welcome back.