If you're looking at just FPS then no, a single 980Ti isn't as "good" as dual 970s in some games (it's 6 FPS lower in Shadows of Mordor, but same in Witcher 3). However, looking at the cost, power consumption, and issues you get with Sli, if you're upgrading from a 770 and willing to shell out the cash for dual 970s, there's no reason at all do to that. Just get a 980Ti and live with your 6 less FPS in Shadows. The only reason to dual 970 is if you have a 970 already and want to upgrade for $330 more.
If you get a 980Ti now, that will future proof you. Dual 970s is going to be a stop gap. A single 980Ti now will allow you to run dual 980s in the future.
Edit. MSI is the best all around in both, Asus has the fastest OC if you want to go that route, but you pay for it in power and heat. I'd go MSI. Clock speed isn't everything, look at everything (speed, power, temp, OC ability) all together.