Hi,
I have a Supernova2 that I got for a great price about 18 months ago, including the 1" pin jaws, 50mm jaws and screw chuck fitting.. When I bought my CL4 s/h a year ago that came with another Supernova2 so I have a great setup allowing me to swap to the relevant jaws very easily. A great addition is the 4point drive centre that fits in the 50mm jaws.
I don't think there is much difference between the Sorby and the Supernova 2 either in price or performance. In the end it comes down to personal preference and backup from the supplier.
My woodturning club has the Versachuck, that is a bit heavier, being designed as an engineering chuck, but can also take a wide range of jaws. Again I think this is around the same price point, +- £130 depending on current offers.
Hope this helps,
Mike C