I use Fanatical not only for their great bundles (which are always a great buy and find whenever they post up new ones) but for their low prices on games from AAA titles to new indie games.
All of the keys you purchase from Fanatical are 100% genuine and are not sourced from elsewhere (as certain competitors do). You know what you're buying is legit and do not have to worry about any repercussions such as your key being revoked and whatnot.
Not only do they provide some of the lowest codes around; but they also provide customers with great discount codes from time to time, along with the addition of a 5% off your next spend voucher every time you purchase with them.
Fanatical is one of my top game key websites alongside a few others. I can highly recommend anyone who purchases Steam games to check out this website before purchasing on Steam!