Hard to say that without some kind of concrete proof. Up to this point all we've had is heresay and grainy videos (as mentioned by many others). At a time where we all have cameras attached to us, if people were getting abducted and seeing aliens and spacecraft, you'd think we'd have something better? The argument that goes against this, is that they don't want to be found, and they are so advanced that they know exactly what we're doing at all times etc. so it's hard to say.
It's totally possible that everything we've seen or heard about up to this point is speculative or bullshit and that we actually are alone in the universe, but I too think this is unlikely, but certainly possible. The vast amount of space in our universe is impossible to fathom.