If you are looking for more challnging questions, LSAT is *definitely* tougher. Realistically, if you are looking for questions similar to the ones on actual gmat, OG11
, GMATPrep and PowerPrep are the best.
P.S. To be honest, Kaplan
sucks for verbal. Their questions are not even close to actual gmat questions, and a lot of times they are badly written. I highly recommend you to go with OG11
. I have not tried 1000SC and 1000CR, but I hear they are good.