I wholeheartedly recommend extra gmat questions. You can buy them from mba-dot- com
To be honest gmatclub math is good, when you need to grind a lot of extra hard tasks (on real GMAT you'll get much easier ones). But for a taste of real questions, nothing beats the GMAT pret. software + extra content for it.Kaplan 800
, imho is not too hard, but too lengthy instead. Every task is obfuscated by weighty phrasing, but underlying math is quite simple to be honest.
Manhattan SC was fantastic, as for math - I never tried it, so can't really help.