They're very evenly matched in terms of quality. I had the older 2010 (not i) and the smaller Diamond 9.0 at different times so I couldn't make a direct comparison but was equally impressed by both. Personally I'd go for the Diamond 9.1 or even 10.1 of which Richer Sounds have a few pairs left at £99. I think both of those models look nicer than the 2010i and Wharfedale have years of experience of manufacturing the Diamond series which have recieved excellent reviews.
Thye bottom line is that both the Diamonds and the 2010i are as good as you'll get for the money and I think you'd be happy with either or.