Of the guns I've shot in full auto, I'd have to say the M60E4 was the most fun, followed by the MP5, then UZI, then M16. Sten was uncomfortable and Thompson was heavy
The most practical would probably be an M16. The MP5 is incredibly comfortable and easy to control though. The UZI is a hose
Of the ones I HAVEN'T shot and will probably never own unless I become a dealer... Kriss Super V and P90. I've heard VERY good things about the full auto Super V but I can't see how a semi-auto one is much of an improvement over any other carbine in the same caliber.