GTX 970 has limited VRAM and you may hit that limit. The 6GB GTX 1060 or 8GB RX 580/480 are much better options and are younger meaning the electronics is less likely to die from age. And as others mentioned avoid 3GB GTX 1060 due to VRAM but also due to lower performance.
Looking on Polish allegro on buy-now offers there is few 1060 6GB from 130 EUR. There is a lot of 8GB RX 480/580 starting from 90 EUR (and 3,5GB GTX 970 are bit higher while being inferior). Bid auctions (like on ebay too) could yield lower prices if lucky - and the only way to fit GTX 1070 or Vega 56 in your budget.
It all comes down to price. The difference for non-high-end setup will be small. And WoW scales nicely among at least few cores. The game doesn’t have any obsession with single threaded that much and the OP is on a tight budget so GPU would be the element to focus.
Some of my benchmarks: