From a guy with all three, my honest opinion:
ROTOR - Sucks. Its ridiculously heavy, needs manual anti jamming to actually get shooting again (taking hands off your gun/pods). Oh, did I also mention how stupidly loud it is when you run out of paint.
SPIRE - Works perfectly tbh, it only has two issues. 1)Price, being new it's nearly impossible to buy secondhand. So you will be dishing out well over £100 for it. 2)It's damn ugly. Admit it. It looks like a cheap boat sitting on top of your beautifully milled marker.
Z2 - Looks sick. Beginning to crop up secondhand cheaply. Never jammed on me (well that I had to sort out, it auto unjams in seconds). It has never broken a ball (unlike the rotor.) Frankly, this is my recommended choice. The only issue I have ever noticed is in the nose cone, it occasionally gets one or two balls stuck. When you are shooting a good few hundred balls per game this barely makes a difference though.
But hey, opinions are opinions. Have fun slating me if you really want to ;D