I own the GSX650F and love the smooth inline 4 over the v-twin of the gladius. The GSX will do long-distance travel no problem, but it's not a very popular bike so accessories/parts are not as widely available as I imagine they would be for the other bikes. The bike is pretty heavy too, which is the only thing I dislike about it.
Haven't ridden the Ninja or the FZ6R so can't offer opinions there.
Haven't ridden the Ninja or the FZ6R so can't offer opinions there.