I’m a big sportbike rider but got a DR-Z400sm just recently (Thanksgiving) and OH MY GOD it’s fun to ride! It’s not just fun, it’s got a lot more pep than a 250cc but it’s still perfectly beginner friendly and very easy to maneuver. It’s not a great highway bike (no fairing or windscreen), but for around town and in the twisties it’s fantastic.
To be honest, I actually don’t have a big vibration problem with my DR-Z. I’m perfectly happy at 60mph, whereas a Ninja 250R gets pretty vibrate-y at that speed. Then again, it might just be that the DR-Z vibrates with greater amplitude and lower frequency. I guess it’s like sitting on the washing machine vs. sitting on a vibrating cellphone.