I'd go with the single 980ti, if only to avoid SLI-related issues. Don't know the numbers off the top of my head, but performance between the two given setups should be comparable. The 980 will also save you from having to deal with the 3.5gb vram issue on the 970's. Granted, not a huge problem except in select situations, but the 980 will be more future-ready and you'll have the option to SLI it in the future. For about the same price, the 980ti offers better long-term flexibility.
Agree, why max out from the get go, get the 980 or if in budget the 980TI, that way you'll have a straight forward upgrade path, the 970 will be better than a single 980 but then you are really stuck as far as upgrading, and as new games come out they will require more and more resources