I disagree.
Meeting Alien could be maybe more interesting.
If we assume that they use the telepathy (or something similar) for communication, it could be really exciting. Of course - the basic assumption that we go out from this meeting with no damage. On the body and mind.
Aliens is a magical creature. As a gateway to hell. As final answer to the unspeakable questions. Such a meeting could be a metaphysical experience. More interesting that we could remember them later.
Meeting with the Preds gives the possibility to communicate on another level. More mental than philosophical. In this case, we hope the dialogue (in the classical sense).
For me personally, every option seems to be fascinating.
But because I prefer classical type of communication and Preds fascinate me a bit more - I choose Preds.
As always.