I'm looking for a not-very-expensive synth, and the ones i've found are, basically,

Roland Juno-D
Yamaha MM6
Roland SH-201
Korg X50

I've never had one, and barely don't know how to use them (Yes, i'm a totally new in keyboard/synth world!), so if someone could help me to decide wich one would be better, that would help a lot.

I'm planning to play in a rock (progrock-metal) band, wich one would fit better?