Without talking about specific ones you've mentioned there, there are some that i'd be open to for sure, and others not so much.
I don't fight with the "exist or not" debate so i'm probably, or at least should be, more open and receptive to the occasional strong story than others could be.
Must say i don't for one minute think these animals are loveable cuddly Harry's and i also firmly believe that the US Government knows about their existence (they have to) so even though i wouldn't just simply fall for anything where those two things meet, i don't completely discount them immediately personally, no matter how far fetched they appear to be on the surface.
I also think people exaggerate a lot, but that doesn't mean that they're actually lying about an experience/encounter, or at least the guts of it anyway.