Not wishing to get into an argument over which software is best, but what does UBB.threads offer that can't be achieved with SMF2 and a portal addon such as Tinyportal?
UBB appears to have a gallery and portal system built in. This same thing can be done with SMF, and you'll have a choice of portals to install, and bridging with Coppermine etc.
If you haven't done so already I would recommend you build a couple of test sites on your server, or locally on your PC using Xampp, then you can try out all the options and see if anything fits your needs.