The one that fits your skill level. A beginner on racing skies going down a black diamond run isn't going to learn much or have much fun, and he is probably going to get hurt. Same with motorcycles except pavement and oncoming traffic isn't as soft as snow.
mr big about covered all in sport bikes except the high dollar BMW 1000cc sport bike. I am told that the 600 through 750 bikes are the safest and most fun because most of the sport bikes with more displacement are over powered for most people .. guess it all depends on your taste . I went from performance bikes to a harley .. Not fast at all and yes over priced but still a lot of fun to ride