I'm not big on the EV Zx line, but there is nothing wrong with them.
The KW122 is a great powered 12 and is in fact on my radar for purchase this summer.
I haven't heard the JBL STX, but they replaced the SRX .. one of the best overall passive speaker lines out there. They sound good, get spooky loud and are useable as both mains and monitors.
So if powered is what they want, go with the KW (or a slew of other quality speakers from RCF, etc.). If passive, I would vote for the JBLs.