I've read some posts in the internet that to prepare the GRE Math Subject test, one has to go through all questions the Stewart's Calculus book. I have a copy of the Thomas' Calculus, which is quite heavy and contains tons of questions. I am not quite sure if there's any difference between using Stewart's or Thomas' in preparing for the exam, because to me, both are focusing on the application side of Calculus. Is it fine to use Thomas' Calculus instead of Stewart's.
Also is it fine to use Apostol's book for preparation.
My point is that if there's no difference between Stewart's and Thomas', then I would spend the money somewhere else because both are 1000+ pages and I don't really want too many books on the similar topics.
If you plan to do graduate work, it would be bizarre to spend any time reading non-rigorous books like Stewart and Thomas.
I think Vols. 1 and 2 of Apostol cover the calculus part of the GRE well, but the page count is a problem.
I presume you've studied most of this material previously, so the problem will be to zero in on the parts you don't know as well. I would probably buy a GRE prep book with practice tests to identify the subjects I had difficulty with. Then I would read Apostol on those subjects only.