Well, 280 comes at a lower price, gives similar performance, has 1 gb more of ram and much wider bus.
It has higher power consumption, heat is not a problem if you buy something like Saphhire's R9 280. (which I own)
While gaming, it runs at 50% fan speed which is barely noticeable (This is subjective tho) and at that fan speed it runs at 64C at factory OC, 68-70C at 1150/1500 OC
960 is ofcourse somewhat more expensive, runs similar to 280 except in some games which require a lot of VRAM for textures (Shadow of Mordor, I'm looking at you)
It has physx and shadowplay (AMD has GVR which works great, just tried it out today, works lovely, i forgot to turn it off for two hours, got me 10+ gb of video but I didn't see an impact on game performance in Metro: Last Light)
960 is just not that price to performance efficient as 280 and the differance in power draw shouldn't concern you unless your local rates are high.
Personal opinion: Sapphire R9 280
I was in your position two months ago and I wen't with R9 280 and I love it, no issues with drivers, I actually installed beta drivers and got 10FPS more in FC4 at ultra. from 40 to 50 average fps.