yea chess master is way tougher although i can beat masters and solve the rubiks cube i say beating a master is more challenging
Which is harder: Playing a chess master or solving a rubik's cube
I'm going to take another approach with this and say that it's harder to play the chess master since there are less than 300 of them in the world, and I personally don't know any, but I can pick up a rubicks cube at Wal-Mart for a few bucks.
Less than 300 ?
This includes all known National Masters,Senior Masters in USCF and all of the FM,IM and GM's in FIDE...these are only two of the chess sanctioning bodies, where did you get your figures?
There are currently ~1200 GMs, 3000 IMs, and countless FIDE, National, regional, district and other masters out there.
I saw something that said there are less than 1300, and I just left out the 1 by accident.
Oh, the title actually asks about chessmasters, not grandmasters. Either way, rubicks cubes are much cheaper and more plentiful.
Solving three Rubik's cubes - while juggling said cubes - and while beating a chessmaster. I'd like to see that. 
All you need to do to solve a Rubik's cube is memorize several combinations. It literally takes like 2-3 hours to learn.
I think one can go to a toy store, buy a cube, and look up the answer on the internet than one can find a master.
I can solve a cube in 35 secondes and i've been cubing for 7 months. I can't beat a chess master and i've been playing for 5 years