I've worked a little bit with each. I find Mikrotik more complicated to set up, but once running seems very stable (I have a Mikrotik router/firewall at home). Ubiquity has more of the "package deal", where it is more plug-and-playin my opinion. Probably better for beginners with wireless bridging.

That all said, I will probably look at Ubiquity for my next upgrade on my 400 foot wireless link (running a form of DD-WRT now)

So, summary:

Mikrotik - more complicated to set up, but more powerful options and features.

Ubiquity - more of the complete ready to run package - but you get what you get.

Both are good, way better than any store bought "router" solution.