Why? Any objective differences or totally subjective/subconscious?
They feel like they roll better but that may just be due to the fact that the hub bearings are new. They also don't seem to feel so stiff (with the same tyres) but again I realise that may just be a subjective thing. Some people may prefer stiffer.
The Novatec hubs are really nicely finished for £60 a pair. The bearings are easy to replace as well apparently, although I obviously haven't had to do this yet.
At the end of the day a lot of my preference is also probably based on the fact that I built the Novatec/Open Pros myself and I know how they have gone together and how to fix them if need be. Anyone building their own wheels will know what that feels like.
I have two sets of Mavic Ksyrium Elites, one older set is no longer usable because a spoke pulled an eyelet out of the rim and they are no economically repairable. The newer set which came with my Scott CR1 have an upgraded eyelet design and have been fine.
If I had £300 to spend on a new set of wheels I would go for handbuilts now over factory even if I had to pay for a wheel builder to build them for me.