The Apple Blog does a head-to-head comparison of Querious and Sequel Pro (successor to abandoned CocoaMySQL) and it looks like Querious wins:
When it comes to MySQL 5 servers, Querious matches and exceeds the features of Sequel Pro with style. If you don’t need to connect to a MySQL 3 or MySQL 4 database, Querious is just more polished and feature-rich than Sequel Pro and is well worth the small price tag.
… well, as long as you don’t need to use MySQL versions 3 or 4.