Idk...all of them are cool.
But I WOULD NOT recommend TnR. Although the method is awesome, its quite impractical. I haven't performed this trick at all. :/
But then again, that's just my opinion.
Witness is a cool, simple, easy trick.
Believe is kind of intermediate, unless u practice a lot...which would ruin a deck or two. But the good thing is that its impromptu.
Distortion is cool. If you like using gimmicks, then get it. Its super visual. If you do get it, watch the DVD first before u play around with the gimmick, or else chances are that you will ruin the gimmick. Trust me, I learned the hard way.
Out of all of those, I would choose witness. It's easy, its simple, yet its hard-hitting... but that's my opinion.
Read the trick descriptions and find out what trick you really want to learn.