R9 280 or GTX 960?

Solution
GTX 960 is a better choice than the R9 280. R9 280x is a better choice than the GTX 960. Both the 280x and 960 are somewhat evenly matched, so depending on game title, resolution and other hardware considerations, either card is probably a good choice for the money.
GTX 960 is a better choice than the R9 280. R9 280x is a better choice than the GTX 960. Both the 280x and 960 are somewhat evenly matched, so depending on game title, resolution and other hardware considerations, either card is probably a good choice for the money.
 
Solution
It's still the same question, and the same answer. GTX 960 (Any)>R9 280. R9 280x > GTX 960.

2GB or 4GB doesn't matter. The GTX 960 Maxwell architecture doesn't utilize the additional VRAM to any great benefit except on a couple of games, or if using SLI, which makes no sense because for the 400 bucks it would cost for GTX 960 SLI you could get a much better single card with none of the dual card issues that plague many current titles.

I personally would rather spend my money for the R9 280x than the GTX 960. The R9 280 is a good card too, but it does not win on very many titles versus the GTX 960 in most configurations.