Hello Raghavendra,

It is good that your participating in Gate exam as you have asked about the Test Series this is one of the best query regarding Gate exam because, most of them fail in selecting the best test series. Remember you shouldn't compromise with the question paper standard in test series because, the tough questions improves and builds your thought process over the given concept.

So I'll suggest you to select 2 to 3 test series to improve your confidence as well as way solving. The test series are :

1) ACE ACADEMY

2) GATE ACADEMY

3) MADE EASY use these test series atleast for the Aptitude and Mathematics.

And for your core XE paper you can appear for below 2 test series:

1) Grade up (Test series & mock tests)

2) Endurance Engineering Academy

Still many more are there but I think these test series are best for you to practice and achieve a good rank.

Hope you have no doubts regarding your query.