I say one 12' stand if you own your house and don't plan on moving. Otherwise it will just look like a fishstore wall. I think if you have some skills a one piece stand and single canopy could look very nice. Same wood top and bottom, trim between, giving the tanks an "built in the wall look" Even if you don't join the tanks you can always build an aquabridge.
Joined it could look similar to this though:


I have been seriously considering doing it and almost started WW3 when I brought it up a few weeks ago with the significant other. I was also considering a custom stand with two 125s shaped L in a corner, if done right I think it could be faked to almost look like a single unit.