Both are great, Gigabyte is supposed to be both faster and quieter according to benchmarks, but I am still currently waiting for my 2nd replacement since the ones that came in had bent heatsinks... so I dunno. Lol.
Both are greatcars but i would prefer msi gtx 970 gaming. Beacuse it will run on 0db when your temps are aroun <65C° belive me they are extremely quite! Even at 100% fan speed. Mine runs at 32-40C° on idle and with the fan not moving, the card runs max 50C° when im gaming on ultra settings still withe fan not moving.