It's difficult to make the statement 'I believe in UFOs'. A common misconception is that 'UFO automatically means 'alien ship'. It means, merely, unidentified flying object. Now, that has become shorthand to mean alien spaceship, but the term is used in other contexts where you can't be sure if that black dot on the horizon is a bird or a plane (or superman), and in some aeronautical circles means an an aerial spacecraft that is as yet unidentified by type. At my local aerodrome, we often use this shorthand to say we don't know if a plane is military, private or public.
I don't believe UFOs are alien spaceships.