I raced IJSBA for 10 yrs and walked away with overall 1st in Stock and Modified in TX running a Kawasaki. I have 2 Ultra150s and love them. Most rental places use Yamaha as they seem to be the most durable. 4 strokes are replacing 2 strokes for environmental reasons but I have no experience with them. I've ridden SeaDoos as well and had no problems but they were harder to work on - Kawa seems to be the easiest IMHO.