the X-250 without a doubt. Match it with a good tube amp and enjoy music.
If You have plenty of money, buy X250 or better X350. I agree that X250 must be better because of extra power. But I don`t think the difference of these two are so big. Probably You don`t hear any difference in blind listening test (normal listening level). Maybe You can hear the difference with more complicated speakers like Verity Parsifal but for Contour 3.0 the X150 will be more than enough. X150 shares the same technology and parts as X350 and has twenty mached transistors for each channel.
But if You have this opttion maybe You can compare these two amps in Your sistem with Contours.