UBB and Eve are very different products. I happen to really like both, so I'll try to take a stab at this for you.
With UBB, hosted by Mindraven, you get Full web hosting, with Member Area access for a UBB. UBB is a great product that includes calendaring, gallery, portal page, and much more. It's customizable and very modifiable. It comes with great support and a close knit community that knows it well. The guy that owns the company is actually here listening to you. The downside, is the same as with any downloadable. You have to download and install or maintain it. Mindraven offers these services at additional fees. That's pretty industry standard and the fees are more than reasonable or competitive. I'm continually telling Rick that he's too inexpensive
Eve is very different than UBB. It's built to be tremendously scalable and stable. You don't download or install it, it comes all setup. You never have to do updates, that is all taken care of for you. If you know CSS really well you can do amazing stuff with it in terms of look and feel, but as you don't get the code you cannot modify features. It also doesn't come with web hosting of any sort, so keep that in mind. Pricing is competitive, starting very inexpensively. As with UBB the guy that owns the company is working on it and available to listen/help/talk to.
Both offer photo galleries and premium memberships and great support and stability and a full long list of features. Both are terrific options. You just need to know what your actual needs are and chose the one that fits best.
You need to determine your needs and go from there.
Do you need full featured hosting?
Do you desire the ability to have threaded and linear discussions?
Do you mind installing it and doing updates?
Is modifying the code important?