The best recommendation is to go with an online test series like GMAT Prep, Manhattan or e-gmat. Since the actual test is adaptive in nature, it is really very important to go for a test which is adaptive and avoid any paper based tests.
GMAT Prep ( Free tests) + GMAT Prep exam pack 1 and GMAT Prep exam pack 2. These official CATs should be more than sufficient. For non official CATs, Manhattan Prep's CATs are second best after GMAT Prep's.
However, here is a comparison of 8 test series available online. List of available Practice GMAT Tests