Seasonic is a great PSU. The XFX is the Black Edition, I think, which also has pretty good quality components. All things being equal I might go with the modular model since that means less cable clutter.
Can't go wrong with 10.0 performance rating and 9.5 build quality rating. he takes off points for functionality for the Seasonic being semi modular which i don't understand as unless I'm sleeving cables I;'d much prefer semi modular. Can't see the point of having a modular 24 pin cable, can you ? I haven't done any builds where I left that cable in the box . Full modular unnecessarily adds cost, adds resistance and introduces a potential failure point. the thing to watch out for is when someone builds off another platform and eats the cost going from semi modular to full modular, what has to "get sacrificed" as part of the meeting price targets. Looking at what is available for XTR, hold up time and ripple were disappointing and it fell short of the previous XFX Black Edition.
XFX has been redesigning and reissuing the PSUs lately and that always makes me jumpy. I mean PSU, Monitor, RAM, GFX card manufacturers have habit of coming out with a new PSU and sending it out to reviewers. And then after they get the good reviews, they switch to cheaper components and don't change the model designation. Other times, they do change the model designation and when it's not sent out to reviewers for testing, I have no idea how it stacks up.
The XFX XXX, B;ack Edition and Pro series had some PSUs that were the equal of the Corsair HX series / Seasonic M12 series; others weren't. Similarly, the XFX Core Edition had a few very good PSUs, not up to the standard of the HX and M12 but matching the S12 and the TX V2. The Seasonic G2 is up there with the HX and M12 series above the TX V2 and S12. Where the XTR fits in I am not quite sure as it falls into a spot lower than the Black Edition and perhaps above the Core Edition.
You will likely find the Seasonic being slightly more expensive than the XFX XTR unit, Seasonic usually sells their units for a bit more to avoid cannibalizing partner sales, I'd go for which ever one you can get cheaper.
Both units are priced at $99.99 CDN on Newegg.ca (I live in Canada).
Both units have the 80+Gold designation. The Seasonic unit is semi-modular whereas the XFX unit is fully modular and both have 5 year warranties. I believe the XFX unit comes with 2 more sata cables than the seasonic unit.
In the end, I think I'm going to go with Seasonic, just because of the name. I've read a few good comments concerning their customer service which is supposed to be great. But who knows, XFX customer service might be just as good. I do not know. Since I have to make a choice, I think I'll go with Seasonic though I'm pretty sure one is just as good as the other.
Gold Designation .... absolutely meaningless with regard to performance and reliability. Only tells you that you will save a few cents a month in electricity. Something ya folks up north don't have to worry about with all that cheap hydropower.
I read somewhere .... that an XTR unit was missing stuff in the box like a manual and a warranty, don't recall where. The Seasonic will have a few less potential failure points ... the cables that are not modular can't accidentally get pulled out and it's not like ya have the option to leave those in the box.