Startide Rising is the best of them all.
Sundiver is quite good too.
The later books were deeply marred by Brin’s giving into pressure from his editors to centre them on a group of adolescent males of diverse species because his publisher was of the view that the average scientific fiction reader was a 14 year old male. Brin has written about this and how difficult it was for him to write outside his natural quite adult style. His fantastic characters from Startide Rising are pushed into the background and only get to step forward and shine again at the very end.
As much as I like to see elements from the Relaunch novels brought to screen, in this case I pretty much knew where the chase was leading, based on the final Voyager Full Circle novel, and that took away some the wow factor of the contact with the 10C.