I saw a U.F.O. once--and that's by the traditional, or original meaning: Unidentified Flying Object.
Truly, a "U.F.O." can be a plane or bird or whatever you just simply cannot identify. But, of course, it took on the 'space ship' connotation, as if one already knew that's what it was. And I've grown to dislike the stigma associated with all of that.
I reasonably believe there is life on other planets, and that there are extra-terrestrials who did not originate from this earth, and are not connected with us. I believe there are some which are not at all human, not at all Carbon-based; as well as those which are human.
Anyway, the U.F.O. that I saw once was triangular in shape, and intuitively told me it was a Stealth Bomber from the local Air Force base. It was at night, it had a point of light on each tip, moved very very slow, was extremely quiet, and either very low to the ground where I was, or was really big. I could see the stars through the middle of the three consistent points of light on the tips--and I reason that, whether or not it was a Stealth Bomber, it had technology that was as simple as 'a camera mounted on top, to broadcast what is seen above...to screens lining the bottom'. I don't know how else to say that. Either that, or transparency technology (except for the three light points).
What it wasn't: three separate objects.
I saw another kind more recently--in the last two years. It was more...hmm...'capsule' shaped. I didn't see it long. Seemed of a light coloration, though, and was at quite a distance from me (unlike the other one I saw years prior). I saw it one night while I was out with my telescope.
I believe my grandmother saw an alien once--surprisingly very tiny.