I personally really, really like 140 rads, as you get a lot more usable surface area by simply making the radiator wider, but not a whole lot longer... For example, a 3x140 radiator (using basic math) has slightly more surface area than a 4x120 radiator; then when you factor in needing only 3 fans instead of 4, you have one less "dead spot" due to the fan hubs (further increasing usable surface area).
The problem for many people is the lack of fan selection, although I think that it has gotten significantly better even just over the past year. I personally think that the Bgears Blasters (140mm 1800rpm 103cfm/3.5mmH2O - rated specs) are just about the best 140mm radiator fan you can get for the money, although NoiseBlockers and others are also quite good.
Also, I have found (at least with my EX420 using 6 of the Bgears in Push-Pull) that the Phobya 140x140x7mm Shrouds/Decouplers work exceedingly well at reducing noise, preventing ANY air leakage, and giving a *slight* performance gain... At least that is true for the EX series, which is 19-split-fins-per-inch, and may not hold as true for lower FPI radiators.
The UT60 280 would be, in my opinion, the best radiator for your needs. One of the "coolest" (haha, I made a pun-ny!) things about it is that, likely due to the massive amounts of copper used in its construction, cooling ability scales almost perfectly-linearly with fan speed! Therefore, buying fast fans and a fan controller would allow you to have nice, low, quiet fan speeds for 24/7 use but crank them up and give your loop some serious heat dissipation ability! I personally have a UT60 240 (didn't want to lose a front intake fan on my Switch 810 in order to fit a 280), and I went with the beastly Koolance 120x25mm 2600rpm fans (spec'd at 107cfm and 5.4mmH2O) in push-pull, and when cranked up they move an insane amount of air!
Point being, I would go for 140mm rads over 120mm rads any time I had the option!