Probably the UT60. Reason being primarily the lower price, the more compact
dimensions (6 mm less wide can make a difference, depending on your case),
equal performance, the protective bits of metal that prevent you from screwing
your bolts into the tubs/fins (I actually have been there

) and depending
on your loop, the two G1/4" threads that go straight out of the end chambers
(can make life easier and a loop neater, depending on your situation).
However, I actually really like the stamped look of the XTX, and for that reason
alone I am (hypothetically speaking

) not yet fully on side AC's side.
Damn it, this is hard, even hypothetically! Must be even worse for you :lol:
Do you have the room for an Alphacool Monsta Radiator with push/pull?
If you do, I would consider that as an option as well. If you want to run
one of those rads without insane fan speeds they should have push/pull,
which takes up a lot of room, but that setup would actually offer a
measurable performance benefit.
I have only found
one review that tests the Monsta in push/pull,
and it's in German, but I'm sure you'll be able to figure the graphs out (the
first one is 3 fans, the second temperature graph is 6 fans)

.
If I had free choice I might also consider the SR-1 (I have bought the
560 version, after all), but price/performance on those is not very good.
I just
really like their looks and am a sucker for stunning build quality,
for which they have no equal that I know of.