Budget budget budget. If its a lower end budget, I'd recommend a MSI 970 Gaming MOBO and a FX6300. Thats what I have for my 970, runs great. Mind you, mines on water cooling at 4.6 GHz. Add in water cooling if possible or just get a FX 8350.
There's always some wiggle room. Theres alot of motherboards to pick from. Just do your research and find what works best for you. Also AMD is a good choice for budgets.
There is a difference between the absolute best and what is practical. For a good gaming rig with a GTX 970, the most popular choice of cpu would have to be the Intel i5 4690K with a Z97 chipset motherboard. Sure you can get an i7 4790K but you don't really need it for a single 970. As for which brand of motherboard, this may help http://www.tomshardware.com/reviews/best-intel-amd-motherboard,3902.html