ZR Tremolo. No Question.
I've never been happier with a trem since I got my S470DXQM. The ZR, like Rich says, is ingenious. Eliminating knife edge friction is the best thing to happen to trems in a while, and it's long overdue, imo. You cant beat the fluid feel of the ZR, it just feels "correct". Everything feels more organic, and the flutter, oh the flutter..
The pitch return on the ZR leaves nothing to be desired. I go ab-so-lut-ly ape sh*t on that thing, and boom, Im back where I started, in tune.
The backstop is coveted tool, and the ZR sporting one must please alot of people. I don't use them, and took mine off immediately, you lose nothing in doing so. But it's there for those who want it, and it works.
The shape is ergonomically friendly, and feels food against your palm. It also looks damn sexy imo.
Did I miss anything, oh yeah! Setup is a breeze! Included intonation tool is priceless many will agree. Also, backstop can come in handy during setups. I also like the ability to adjust arm tension at any time. That also reminds me of the ease of adjusting spring tension, also available at any time.
I rant and rant about this thing, cause I love it. It's a floydist's dream, and a beginner's friend, it suits all.
Now, just add this to 24 frets and an alder body, and boom, you have my dream guitar. Hey Ibanez, I'll be your best freind.... (For now im thinkin retrofitting)
Love to support my ZR!