+1 with what hypertech says. The XTX50, XTX100, and XTX200 are all the same except for a couple of cosmetic pieces - stickers and slightly different plastic covers.
The first stages are that way, too... Internally, the DS4, XTX100 first stage and XTX200 first stage are identical, too... Except that in some models there's two high pressure ports instead of just one. The XTX200 first stage is actually mounted upside-down as compared to the other two. All of them are excellent, with the biggest difference being cosmetic.
Personally, I prefer the diaphragm on the first stage to be mounted UNDER the first stage, as it is on the DS4 and the XTX100 - it just appears to be in a safer spot than on the XTX200 first stage. However, I've never had a problem with the XTX200 first stage that I own, even after thousands of dives on it... And I dive in pretty rough conditions. So they're all excellent.
The location of the diaphragm is the reason why I like the XTX100 so much - but really, it's just a cosmetic thing, as clearly it's not a problem. I like the DS4's "hiding" of the diaphragm also, but the hose routing (tilted ports) on the XTX100 and XTX200 first stages is a little cleaner, IMHO.
That said, most of my regs are DS4's - the price difference is tough to justify for a little angle in the ports.
I'm not a fan of the LCD screen that tells me when they're supposed to be serviced - you may be, but I'd be frustrated by a reg that told me that it needed to be cleaned, since I typically run my regs waaaaay over their recommended service intervals. If I had that screen on my regs, it'd start screaming in less than a month - 'cause we dive full-time for work.