I think they all have potential for getting a message across. I've seen Xtranormal used for library conferences and also presentations during Orientation Week at university and I think it has so much potential for helping us engage with students. My old workplace used it for Orientation Week because students hadn't been responding to previous library presentations (not surprising given the amount of new information students have to process during Orientation) so they tried something different and for the first time students really paid attention to what was being said.
I really liked MakeBelieveComix, just because it was so much fun to create something and really simple to use. My partner and I can both see ourselves spending a lot of time on this site. I think for libraries it could be very useful for making a short point but in an interesting, humorous way. You can view one of the Comix my partner and I created here