msi gaming gtx 970 (just bought it to replace gtx 660ti). GTX 970 is by far the most popular card at the moment, it has #1 spot on futuremark hardware, and on this forum as I write this there are 23 gtx 970's, next highest is gtx 980 with 11. I'm surprised actually that the R9 390 isn't more popular, only 5 here, it has better raw numbers than the gtx 970, especially ram and bus speed (8g vs 4 g / 512 vs 256) and is priced about the same. I bought the nvidia card specifically because of it's lower numbers actually, the fact that it competes with the r9 390 using generally lower stats for me is a sign of good build quality and good optimization, not to mention the lower power draw and temps. I've never had problems with Nvidia cards either, the same can't be said for AMD.
edit: not trying to start a war here, AMD also makes great cards, it's really more about preference.