The software only really differs in aesthetics, button placement, and sometimes the random number generators. All of the bigger sites like Full Tilt, Pokerstars
, Ultimatebet, Bodog, etc use pretty solid random number generators. The things you notice are likely only due to a small sample size of hands seen. For example, I just freed up my Full Tilt account, and had quads about 5 times. I don't think they're more likely to come as much as they just happened to come a lot in the short term. I'm sure 200k hands later I won't be getting a lot of quads as compared to other hands.
I've played on UB for a long time, quit a few years ago. My girlfriend plays there now. I can tell you flushes don't come more on there than any other site from our collective experience. I hope this helps.