The prices are comparable once you're comparing aftermarket 290s to aftermarket 780s, and both can be found on sale via techbargains and slickdeals on a regular basis. You will find discounted custom 780s for 450-480$ on a regular basis, same story for aftermarket 290s which I have seen around the 440-450$ mark on sale. The aftermarket 290s do not seem nearly as cheap in cost as reference for whatever reason, but they're still very competitively priced with good performance. The reference is heavily discounted but I would not suggest the reference due to heat and noise; pretty much you NEED aftermarket with the 290 if you want peace of mind. Anyway, I personally heavily prefer the 780 due to software, drivers, features, out of box ease of use, etc etc. The 7970s I owned a couple of years back were generally okay for single GPU but once you do anything outside of the "normal" such as 3d, crossfire (back then anyway) or eyefinity it all went to hell. AMD has improved a little since that time but not nearly enough, I find nvidia's software better so nvidia always wins by default until AMD makes a huge jump on the software side. Is NV perfect? No. Better? IMO, they are much better. The fact that some of these well documented software bugs took 6 months to 2 years to fix for the 7970s, yeah, AMD Doesn't excite me all too much these days. The 7970 isn't the 290, but the same software team serves both products, and the 7970 left a sour taste for me after having used eyefinity. As I said. AMD Doesn't excite me unless they make huge strides there, so we'll see in the future.
Also, GK110 is better when you factor overclocking in. If you look at max OC vs max OC reviews, GK110 is heavily favored. If you OC that can be something to consider. So my nod goes to the 780. But you just buy whatever you want to buy and go with your gut. Ask the internet for an opinion and you'll get a million different opinions. AMD offers comparable performance, very good performance in fact. I find the software end of things to be either bad or questionable, so my answer to that is: what good is great hardware (AMD always does make good hardware) when the software doesn't fit the bill. Reading stories of AMD 290 beta drivers doesn't exactly inspire confidence either, so, whatever. take that for what it's worth as my personal opinion. As a single GPU user you'd probably be fine. I think AMD generally does okay there, but once you step out of the "norm" and into an enthusiast setup such as surround, 3d, or what have you, perhaps problems will arise. And my take on that is a 50$ discount isn't worth having less features than I use on a regular basis (downsampling, adaptive vsync, etc) with potential hair pulling issues that just frustrate you. That certainly was the case with 7970s, I can also find various threads both on here and other forums with similar current issues with eyefinity on 290X, oddly enough. Of course NV isn't perfect. But I haven't had a situation of them taking a year or two to fix anything either. So yeah. Yet another worthless opinion to add to your collection of your opinions here : take this one for what it's worth. That has been my experience with AMD in general.