None of us will be able to provide you with any “secret” information, because the algorithm is… well, “secret”. Fiverr isn’t going to release algorithm data, because people – such as yourself – would try to exploit that information to benefit your gigs.
As far as we know the “Customer Review” option is supposed to rank gigs by customer review. I think this alone would be self-explanatory.
“Recommended” is supposed to rank gigs by a variety of factors – none that we will ever know for certain.
Don’t try to game the system. Deliver quality work that results in positive reviews. This is the only tried and true way of “rising” in the rankings.