Preston is better and you can get it from Jarir and the other one is GMATs own prepration book available on MBA.com.
Any ways may be the information will be little bit outdated as i took GMAT in 2003 and scored 660, just by preparing out of this stuff.

Read tips and tricks for mathematics section carefully for each type of question as it would help u a lot and as GMAT is CBT know, so solve the sample tests on system only as it would increase you ability to concentrate on stuff in screen instead of solving it on paper as it would help you a lot.
Wish u luck for future endeavors.