Superzoom lens

Hello, this is my first post so I apologise if i am asking something stupid or something that has been covered before.

I have a Sigma 18-250 Macro which I used happily on my D300. However, I am thinking about upgrading and want some opinions re whether the Nikon 18 300 (latest version) would be any sharper or faster to acquire focus on my D7100. I also think that it might be best to use only Nikon kit for best compatibility. Opinions please.

Don't know the 18-300m.m just came out recently. But i do have the 70-300 m.m Lens for my D7100
and it takes excellent pictures. So i guessing the new 18-300 will be good.