Here's a pretty good comparison. The suits themselves are fairly different. The panther suit is an evolution of the 89 batman with the musculature and *ahem* nipples. The sonar suit is a precursor to the begins suit with a more technical look and the same H.R. Giger alien inspired designed that continues on from the bat vehicles.
In canon the explanation for the suit change is that the Sonar suit is the only one not destroyed when the riddler blows up the batcave. I don't think, other than the ability of sonar vision and usage of the sonar batarang, there is any other reason to call this suit the "sonar" suit.