It's fairly competitive between the Gigabyte, MSI , and ASUS cards in terms of performance, but the Gigabyte is better for overclocking thanks to it's bigger stock cooler.
To be honest I've never seen any benefit to overclocking GPUs. Some people say it makes a difference, others don't. From my experience of GPU overclocking, the performance gains aren't really that big, and if you've got a card like a GTX980 you aren't really going to need to OC anyway.
I'd probably advise the Gigabyte though, it's stock speeds are higher even if you don't overclock, and it runs cooler thanks to it's huge radiator.
EDIT: I have two MSI GTX970s and the lack of backplate is annoying. My top card sags A LOT.