While i do think life exists elsewhere in the universe, I think the chances of extraterrestrial biological entities coming to our planet is exceedingly unlikely. Space is just too big, and there isn't any hard evidence that faster-than-light travel is even possible.

Although, the universe isn't just big -- it's old. There could be some ancient civilization from an ancient planet that became uninhabitable long ago. If they were technologically advanced enough to escape their solar system before things went tits-up AND were able to live multiple generations fully in space AND they just so happened to set out in our direction, I guess it's possible that they found us. Even then, i would expect any UFOs or whatever would merely be probes, not the actual biological entities themselves.