My choice is no.52 in E flat as well... Polishing it up at the moment.
Lots of flashy bits as well as fast strong fingers!! The slow movement is one of the very few slow movements that i enjoy as well! highly recommended!
In my opinion, no.49 in E flat, as well as the overplayed C# minor sonata, definitely loses out to this one in terms of brilliance, technique as well as interesting developmental devices. I find both sonatas overly repetitive, but they are popular choice for the DipABRSM.