Are you planning to rent or build your own?
I've had a lot of GPU rigs most of which have not ROIed but the last few based on GTX 970/960 seem to be doing ok on X11. The nice thing is being able to sell the parts at 50%+ of original price, which is not always possible with ASICs, plus GPUs tend to have very generous warranties.
However density sucks - lots of plumbing required to build a 4-GPU rig that makes a measly $40-50 per month. Compare to a shoebox-sized S7 that makes $150-$200 a month at this time.
I don't know much about making money from renting, I'm on the other side of that deal, i.e. renting OUT.