Middle Class Karts are fairly descent, I'm thinking about using Bowser Jr. with the Mach Bike more often since Dry Bones tends to get knocked off, or drift into a wall.
Advantages: Have descent stats all around most of the time, don't get pushed off as much, and can recover descently fast.
Disadvantages: None of its stats are usually all that good, don't push as hard as heavy karts, and can't recover as fast as light karts.