Which is harder: LSAT, MCAT, GMAT, GRE, other?

[Redmen62]

For those who have taken any (or all) of these exams, which would you consider to be the most difficult? Obviously a tough question since they test different things, particularly the MCAT, but opinions would be interesting nonetheless.

MCAT vs. LSAT has been discussed before on law school sites I frequent, but those discussions seem likely to be biased (although I got the impression most considered the MCAT more challenging even there).

I've taken the LSAT and know a little about the MCAT. The other two I know little about and may or may not be approprately included in the discussion.