What's the difference between Behringer XENYX 1202FX and the Behringer Eurorack UB1202FX?
The telling part is in the name. If you are not aware, Behringer has had a longstanding feud with Mackie (among other manufacturers as well) about copyright and trademark violations. Behringer has lost at least one of these lawsuits and were forced to change their cosmetic design on many of their mixers.

Their Xenyx series is a not so subtle copy of Mackie's Onyx series preamps. The Onyx series were a noticeable step up from the vLz and vLz Pro preamps. Behringer decided to create their own premium line and call them Xenix. The problem is, I have yet to read a review that states a discernible difference between the UB and Xenyx lines. My presumption is that at this basement price point, it hardly matters.

If you could audition both (many online retailers have a return policy), I wouldn't bother trying to find qualitative differences...I'd just listen for noise floor differences.