I prefer the GTX 770 Windforce OC:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125463
See how these two cards compare from one of the more reputable and consistent review sites:
http://www.guru3d.com/articles_pages/gigabyte_radeon_r9_280x_windforce_review,18.html
http://www.guru3d.com/articles_pages/gigabyte_geforce_gtx_770_windforce_review,18.html
Here' s a direct head to head comparo from gpu boss as well:
http://gpuboss.com/gpus/Radeon-R9-280X-vs-GeForce-GTX-770
I like the guru3d gaming test comparisons over gpu boss but it is all pertinent to your decision. The 770 is $30 more ($339 vs $309) but I'm comparing apples to apples (same exact windforce oc vs the other) and you don't have to get these exact cards but either way I'd get the 770 over the 280x regardless of which manufacturer you go with. You get the best value and spending a little more now you'll end up with the better hardware which you won't regret. You will make $40 up some where but you are stuck with lesser hardware if you don't go for it. Regardless the choice is yours. Have fun! Hope this helps!
Thanks,
Justin S.