I have tested so many centers side by side looking for a nice one for my 590s (until the day I can fit another 590 that is) and so far the THX 365c has been my favorite. Mainly because it is very clear, as expected by its great horizontal dispersion, and also projects it sounds nicely away from the enclosure so you are not constantly reminded of the sounds coming out of the box like the Emotiva C2+ for example which was VERY directional not to mention its other issues.
I was already to call it the winner but recently received the SVS Ultra Center and my opinion may be shifting. On Monday I will finally have the time to compare them fully and make my final call.
Then again, for almost $400 more, the SVS better floor me to make it worth it!