No idea about Nokia 520. But i can tell you S duos is much much better than Xperia U. Xperia u is not a Mid range mobile any more :/ Go for xperia J, P, L if you really need Xperia..
S duos has certain Advantages and the other. Its speed but given Single core processor might not be as quick as a dual core even though it has a 1GHz Cortex A-5. HD video play is not a problem with S duosBad thing about S duos is at times it gets softwre lags. (because its running the latest JB with min. requirements)
Good Luck
Oh ok machn Thanks a lot for the detailed info...
