My 2 cents,
I picked up and played with all three.
The Arca just felt weird. I love their ball heads, use the cube 90% of the time on tripod, but found the tech camera unsettling. Some gear sticks to your hand (Leica S). Some gear jumps away from you like a nervous kitten. The Arca did that with me.
I expected to like the Alpa, given the reports of owners - I'm usually a sucker for insane engineering. I tried the SWA and STC. They both felt limited. I kept thinking "why can't it rise and shift? The Max is too big... " As Guy points out, the workarounds are easy, and I don't do interiors, so would have been happy using Alpa, but went with...
The Cambo WRS AE, which was the least glamorous, was as functional as the Arca, but seemed very easy to use with well thought out controls. One thing that makes the Cambo feel less precise - the zero points of adjustments on tilt and swing have a slight dead space. This is intentional, so you know you're really at zero. It feels loose, though. The rise/fall/shift controls are wonderful, and that's what I use all the time.
But really, the backs and lenses are the same for all three systems, so it just doesn't matter. Get what sticks to your hand!
Hmmm... maybe I should have gone for the Leica...