I never seriously checked out Samsung e490. While buying the st50, I had a good chance to compare the xt50. I felt that the xt50 was very good indeed. For normal tv including hd feed, the xt50 handled incredibly well. At a distance of over 8', there was not much perceptible difference. Only when sharp objects and text was displayed, the fhd panel of st50 shine apart. The st 50 has less reflective surface, better panel, better blacks, better pq, etc., but then we are not discussing st50. Point is xt50 in some conditions performs as good as st50.
Now x50 is same as xt50 when it comes to the pure panel. So I would trust on x50 a lot. Rest is all dependent upon price, features, number of ports, etc.
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