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.