ASICs might not be the answer here, looking at the crappy returns one gets from Scrypt or SHA-256 devices currently. Some Equihash ASICs are promising but probably short-lived and expensive.
Current GPUs make very little per day too.
All of that makes it a bit hard to make a decision. Since this is "free electricity" I think I agree with you "Combo" would be better.
Betcha we're all be turning our heads towards 2070's... Maybe 2080's.
Personally I can't wait for AMD's 7nm (or rather, I have high hopes - which isn't usually healthy).
Waiting also isn't good enough to do on OP's condition.
But I might be waiting for AMD's 7nm.