Here is what I considered before voting for Star Trek. I ruled out series which I know little to nothing about (Babylon 5). In Battlestar Galactica there is the whole issue of the Cylons(sp?) trying to kill humans. That was out. In Star Wars the political state is constantly unstable. Quick, think of a Star Wars game or movie with a stable and just government... there isn't one? In Firefly, love it as I may, the Alliance is corrupt, non-Alliance folk are incredibly poor and live in a, mostly, archaic way and on top of that you have to deal with Reavers, so that was out, too. Mass Effect was my second choice, but the whole Reapers thing made me have some second thoughts on that one... Maybe pre-Mass Effect 1 galaxy would be fun.
Star Trek won out in the end because, while it has galactic threats, they always seem to mostly deal directly with Starfleet. The whole universe seems pretty clean and crisp. Plus, Picard is sweet.