"Horses for courses" There are plenty of great roads for sport bikes around, unfortunatly from Bangkok I have a miniumum of two hours riding to get to anything worth while. But with a nice bike nestled between my legs and some good winding roads, there is no better place to ride a sport bike. For around the city I can barely think of anything worse than a sport bike, so I usually use a small motard, currently a XR 250 Motard or Dtracker. Perfect town bike, light and easy to get around traffic, plenty of pull down low and Bangkoks shitty roads are handled easily with lots of suspension travel and ground clearance.
As for hiring one, no one will hire you one in Bangkok, you can hire in Pattaya but are not supposed to take them out which sort of defeats the purpose of hiring one.