I own the Zeiss RF and I've used the other two. There isn't much difference optically that I could notice, the Leica's seemed the clearest to me by a little bit. I use mine strictly for hunting, which usually means I range trees and landmarks so I have an idea of surrounding distances. I don't often range animals I want to shoot, as there's little time, so all the ballistic information isn't important to me, though they all have that option.
My decision mainly came down to price. I bought a demo Zeiss RF from Cameraland NY for $1750 when they had a sale for CGN members, which was $1500 less than I would've paid for Swarovski or Leica. There were a few little things that also helped sway my decision; The Swarovski ranging button is on the left side, something which felt odd to me. Leica and Zeiss is on the right. The Swarovski has large nubs underneath on both barrels to house the electronics, I could feel them against my chest. The Leica was very nice, but not $1500 nicer than the Zeiss. If I had the choice between all 3, price notwithstanding, I'd probably choose the Leica. It was just that little bit clearer than the others and the rangefinder was more consistent in getting measurements, especially at distance. I can get tree lines out to 1600 yards or so on the Zeiss, the Leica went to over 2000. But then I gave my head a shake and realized that's about 4-5 times further than I'd ever shoot anyhow!
I think once you're looking at this level of optics, they'll all be very similar and it comes down to personal preference. My advice would be to handle them all and decide from there. One thing is that when I carried a separate rangefinder, I rarely used it. Now with the combined unit, I use it all the time, most often playing games of "guess the distance" to pass time. You'll like it, no matter which one you choose!