I would consider myself a decently skeptical person, but I also try to keep an open mind.  I don't particularly believe that Big Foot or the Loch Ness Monster exist, but it's possible that there are creatures lurking in the deepest parts of the wilderness that are savvy about remaining undiscovered.  I don't particularly believe in ghosts either but at the same time I'm not chomping at the bit to go spend the night in a creepy old house.  I'll hedge my bets on things like that.  I definitely lean on the "don't believe" side, but if some sort of empirical evidence were presented that they do exist I'd happily change my tune.  And I'm not going to tempt fate more than necessary by having the hubris to say they 100% don't exist.  But I still don't really think they do.

On the other hand I do tend to believe in aliens.  I don't particularly believe that any have come to visit us here on Earth, but in the unimaginable vastness of the universe where there are literally more stars than there are grains of sand on the entirety of Earth, I do find it difficult to believe life hasn't cropped up anywhere else.  There doesn't appear to be anything particularly remarkable about Earth, cosmically speaking, other than it's the only place we know for sure life exists.  But we know so little about other parts of the immensely massive universe that it's difficult to draw any rock solid conclusions.  I don't know that there definitely are aliens out there and I don't have any more empirical evidence that they exist than I do for vampires, but I still choose to believe in them.

I guess it's the matter of scale that makes the difference.  Relatively speaking the Earth is a teeny tiny place compared to the universe.  We still haven't explored every last nook and crevasse of this planet but people have spread pretty far and wide over it and nobody's ever been able to offer definitive proof of various fairy tale creatures.  Nobody's ever been able to offer definitive proof of aliens either, but we've barely scratched the surface of exploring everywhere that they might exist, so I feel the likelihood is greater that they do.  Still not 100% certain, but I lean on the "do believe" side until such a time as we're able to explore the vast majority of the universe and not see any sign of them.  Which, let's face it, is probably never going to happen.  

It's really, really hard to fathom just how big the universe is.  We've barely managed to send a spacecraft outside our solar system so far.  We're a long, long ways from interstellar exploration.  I think we can get there someday, but even then it will take a ridiculously long time to explore the whole universe, unless we can come up with some kind of outside the box technology that allows for super speed or being in multiple places at once.  That could happen, too, I suppose but for now that's just as much of a fictional tale as unicorns.  

In the meantime I'm still going to sit here and believe in aliens.