I think my favourite rental car depends on where I am.
Due to the lovely roads in BOS, a Lincoln Continental wins out here.
A Jeep Wrangler out of KOA, OGG, or HNL, a can be the more fun, and let you best take advantage of the weather, and scenery.
A Mustang GT out of LAX is wonderful if you're driving up the PCH.
A snazzy sports, or exotic car at MIA could be just the ticket for Miami Beach.