In my view, the first one. Single rail every time for me now.
Unfortunately the current shortage of high power PSUs is a pain in the neck.
I am awaiting delivery of one of these Corsair 1200i's myself.
When it arrives I will put it on to my KNC Jupiter and move the EVGA 1000P2 from that to my pair of ant miners.
At present I'm running the ants on an OCZ ZX series 850W PSU which seems to be working fine but is too close to 100% load for my comfort.
I have already killed a Be Quiet Dark Power Pro 850W on them (was multi-rail) - it lasted 24 hours then went short-circuit across the mains and tripped the ring-main circuit breaker.