I think some people are mislead about keyboards and this game. Mechanical keyboards aren't optimal for WA at all, not to say people can't rope well with them, I've got a Das 3 with MX Browns and they're considered a great all rounder for typing and "gaming", unlike blues which have an uneven release / activation point, if you can ride the activation point on Browns / Reds etc you can have as fast response as any keyboard, but the thing is it's too hard on Cherry switches. I did use red o-rings on it for a while a long time ago but I find 1 it turns a mech feel back into a squishy rubber dome and 2 although it does slightly reduce the key travel I found it didn't help at all with performance.
The key travel is far too long, the spacebar is clunky and wobbly, I've had the Das for 6 years and still can't reliably ride the actuation point because of this. I think they do fine for FPS gaming where WASD etc works fine, but for fast / accurate tapping I'd use something else. The Cherry switches are designed for good typing feel and offer no advantage whatsoever over a standard membrane KB. Of course when they go mainstream in this day and age gaming companies are going to take advantage of it and make it seem like the next best thing, just like 12000 dpi mice running @ 2000hz.
As for PS/2 and USB, PS/2 are technically better (I ran the Das on it for the sake of NKRO, and why not if I have a PS/2 port) as it's interrupt driven over USB polled, so if it's possible to use PS/2, aside from hot plugging it's better regardless, but you won't notice any difference in latency when gaming, wireless I'd avoid everywhere (input, network etc) if you care about stability and latency.
While I'm nowhere near the best roper I like to have a setup for as close to zero lag as possible for gaming in general, like using a CRT monitor with high refresh rate, I have a custom minimal windows XP disk just for WA and Quake that's tuned for lowest latency (Vista, 7, 8 and 10 all have input lag and high DPC latency). I mod all sorts of things to make them better, it's just a hobby really to aim for perfection.
With keyboards I think the scissor switch will always be most optimal default because of the low travel as long as keylock doesn't interfere, I tried roping with mouse clicks before which worked ok for response (I modded the switches inside to fast responding ones) and felt quite natural as I use WASD for movement but I found the clicks just weren't smooth like a keyboard and it felt still a bit slow.
I've tried the paper ball method under the membrane of rubber dome - this one is probably the best mod you can do, but it has to be done right, as you can make the keyboard as responsive as you like (even touch sensitive) but I think you have the get a good hard wearing object underneath that isn't going to shift over time for it to be reliable. This method could probably be unbeatable if you took the time to set it up right.
Standard rubber domes I find vary loads in how sensitive they are, some are lower travel and soft, some are really stiff either by default or where the domes have aged, but they're still in general better than mechanicals because of how fast the dome snaps back.
Last year I switched my Das to a HHKB Pro-2 which has Topre switches and it's USB, I've dental banded them (sort of similar to o-rings on cherry, but they don't affect the feel of the key when bottoming out) which reduces the key travel slightly, I find the Topre amazing for response as they're a mix of spring and dome and make no contact on actuation, they also bounce back really fast with very low tolerance (no wobble / rattle), basically they blow Cherry out of the water for typing feel and key response (makes Cherry feel like a cheap toy).
I've never tried Alps switches so can't comment on them, also buckling springs I haven't tried in so long but I'm pretty sure they're crap for anything other than typing because of how stiff they are, also the Model M has I think very low key rollover (2 or 3 I think) although the Model F has NKRO and also better switches.
Just thought I'd share some of my thoughts on keyboards and stuff, basically in terms of maximum possible tapping speed and timing accuracy, I would say the #1 keyboard for WA would be a decent modded one with an optimal object under the membrane to make it touch sensitive. As long as keylock doesn't come into effect either that or naturally the next best thing would be a low profile scissor switch board.