When you first start riding you want to get something older, cheap and with no more than 500cc, because its likely that you're going to drop it while you're learning. The Kawasaki Ninja 250 is the most popular bike in the whole world, literally. Its the bike I learned on and I have taught people to ride on it since.
are you in UK? if so you'll have to ride a 125 till you get your 'big bike' licence. there's plenty about. i wouldn't even start thinking about a sports bike till you have some experience cos even tho they can be fun they can also bite you on the ar$e! i always like the gsxr's but when i passed my test i got a 650 v-twin. have fun, ride safe. die old!
An older dirt bike in a field or some ditches, anywhere will help you learn how things work before you go street. If that's no option, the Ninja 250s are great starter bikes.