Tom's Hardware's "Best Graphics Cards for the Money" for February 2014 is all Nvidia, literally. Above $190 there isn't a single AMD card on the list, not even an honorable mention.
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-4.html
With that, as an Nvidia owner, you should take a strong assessment of their unique features and ask yourself if you use them and if they have value to you. AMD cards really only have two features, compute performance and Mantle for BF4. Nvidia cards, on the other hand, have PhysX, Geforce Experience, Shadowplay, and a host of unique graphics settings, such as TXAA, FXAA, HBAO+, Transparency Supersampling, and forced Ambient Occlusion. Which package is more attractive to you and which is more likely to enhance your gaming experience?
One last self-assessment should be the state of Nvidia drivers. Have you had a positive experience with them? Are you comfortable with the Nvidia Control Panel? Are your drivers compatible with your games? If the answer is, "yes", I would stick with what is already working for you and be aware that your friends might be only seeing one side of the spectrum.