Of those listed, the JBL amp would probably be the best bang for the buck. For me, it would be a toss-up between the MTX and Kicker amps. I haven't been very impressed with KW's products over the last couple of years. They seem to have dropped a notch in my book. I can't say I'm a fan of RF for any one reason (part looks, part value, part marketing, just never liked their whole vibe despite some good, but pricey, products). The Xtant amp specs out as a nice amp, but is a bit lacking in the looks department if you want some "show" in your system.
I guess after all that, the MTX amp would be the one I'd choose. I like the SmartEngage feature which eliminates the turn-on lead, good crossover/EQ features, and it'll probably put out significantly more than what it's rated at.