I have an X2U and I would not buy another one. It suffers from low volume and higher than I would like noise (hiss) level. It does have high-end features. It will supply 48 volt phantom power, it does not suffer from the dreaded USB whine sound and it supports a headphone connection.
The ACX people have produced a video with their recommendations and they have a microphone and MicPre that they like. I have no personal experience with either one.
I think it's in the first video.
http://www.acx.com/help/video-lessons-r ... /200672590
USB direct MicPres tend to all suffer from low gain. As I posted, overload and sound clipping is immediately fatal to the show and could result in a returned product. Low volume is always assumed to be fixable with enough time and effort and so the product stays bought. Much better (for them) to have low volume.
That's not how I do it. For very nearly the same money, I have a "real" but small, full sound mixer.
http://www.sweetwater.com/store/detail/PV6
That has no such problems as low volume, lack of control or high noise level. This is it doing a broadcast radio sound shoot.
The down side is the operator has to have some idea of what they're doing. It's not plug and play, although sound mixers tend to look more complex than they are. You can generally turn off or neutralize the services you don't understand and they work just fine.
I'm plugging my mixer directly into a Mac which was specifically bought because it has a very high quality stereo line-in connection. If your machine doesn't have that, then you need to add a high quality USB digitizer such as a Behringer UCA202 that I use. This is one with my mixer and a Windows laptop.
This system has also been certified for musical overdubbing should you need to do that.
Koz