With 770 having a fair price and the 7970 single card having addressed frame timing concerns, get whichever one catches your eye.
Tech Report - epicenter for the smoothness reviewing - from their GTX 780 review.
http://techreport.com/review/24832/nvidia-geforce-gtx-780-graphics-card-reviewed
Crysis 3
"This last metric measures "badness"—that is, time spent working on really high-latency frames. Here, the Radeon HD 7970's smaller spikes at those trouble points in the test run give it the edge. AMD's drivers and GPU combine to produce a smoother gaming experience in this case. "
Far Cry 3: Blood Dragon
"Not too many surprises here. The 99th percentile results are all under 33 ms, which means except for the last 1% of frames, all of the GPUs are slinging frames at better than 30 FPS. Even the longest frame times aren't too large: no frame takes more than 50 milliseconds to render, so there's very little "badness" going on. "
Tomb Raider
"The FPS average and 99th percentile frame times tend to agree, which means we aren't looking at any major problems with high frame latencies. A look at the distributions from each card will confirm that assessment. What's left is a very straightforward outcome: the GTX 780 is somewhat slower than the Titan but faster than the Radeon HD 7970. See a pattern developing yet? "
Guild Wars 2
"Although there are some frame time spikes for all of the cards, only the Titan and GTX 780 show substantial spikes in their FCAT results as well as in Fraps. The GTX 680 and 7970 have very smooth lines in FCAT; the hiccups in Fraps are buffered out. As you sort through the various results, you're see the different cards changing position depending on whether we're looking at Fraps or FCAT data and what's being emphasized. "
Sleeping Dogs
"The Radeon HD 7970 pulls off the upset here in our latency-focused performance metrics, followed closely by the Titan and the GTX 780. "