Steam have price matched humble store (gog key). Steam offers a better feature set, including very good controller support.
It was cheaper over Christmas, but this is currently the best price, and I want to play this far too much to wait for the summer sale.
Witcher 3: Wild Hunt, £14.99
Witcher 3: Wild Hunt - Blood and Wine, £9.59
Witcher 3: Wild Hunt - Hearts of Stone, £4.79
Witcher 3: Wild Hunt - Expansion Pass £11.99
There's a Trilogy Bundle too, but it doesn't include the GOTY edition. Witcher 1 and 2 are on sale too, posted separately
Offer ends in 2 days!