Ian gave a good answer to Ray's question.
I'd like to point out my August 2003 column, "Cube vs. Checker Play." I analyzed real data, and found that all top players and almost all advanced players have significantly lower cube error rates than checker play error rates. The gap grows even larger if you look at the actual equity given up rather than EMG. Tough cube decisions are exciting, but checker play decisions involve much more equity overall.
Unfortunately, this has been confused with work by someone else, who showed that adding a specified amount of noise to cube evaluations harms bots significantly less than adding the same amount of noise to checker play evaluations. That's a very different result, but my conclusions were attributed to him.
Douglas Zare