I'd have to really think as to best show ever....
But as far as whats going on now....
And like everything else...not everyone will like the same shows.....been to many a 'hit' that I couldn't wait to be over.
Mystere at Treasure Isl. II
the Blue Man Group (also good if you have kids) at the Venetian
Ka, or the New Cirque Du Soleil show over at the Grand (same show...I just call it Ka for short)
Le Reve over at the Wynn....which as most know used to be my hangout before Wynn bought it out.
excellent show IMO BTW.
DID NOT like Mamma Mia. (its at the Bay....weird)
if you like magic shows, and especially if you're bringing kids, they'll really like Lance Burton as he brings up several kids from the crowd to help with different tricks.
also...if hes there when you visit...without a doubt one of THE best, without a whole lot of techno assistance....David Copperfield. Dude will make you believe the stuffs real.
anyway thats a few I like....