zeogold: Price:
Humble Bundle wins. By a longshot. You can almost always get at least 3 games for just a dollar, and at that, you usually get free Steam keys with 'em, too.
Quantity:
GOG has the bigger selection and older games, but Humble is slowly improving as it gets better deals. You gotta cut Humble a little slack though, because I imagine it's much harder to convince a developer to sell a game as packaged "shovelware" rather than full-price on a store.
Choice:
GOG has the better games, hands-down. Humble has been frequently criticized for bundling low-to-mid-quality indie games. They occasionally crank out a few gold mines, but it all depends.
Customer service:
Gog wins. Not only are they always helpful and looking for ways to improve the community, but they're kind and have a money-back-guarantee policy on games that don't work. If Humble has this, I am not aware of it.
My verdict:
I gotta go with Humble, despite saying this on a GOG forum and despite how much hate I'm gonna get from the fanboys. As much as I love GOG and being able to play games I never could otherwise, Humble is expanding rapidly, and not only do I get free Steam keys with my games, but I can also donate to any charity of my choosing and decide how much of my money goes where. Nobody else lets you do that.
Editing in progress: Typing up typical review style for both GOG and Humble Bundle
GOG:
+1 for having old games
+1 for being committed to DRM-free games
+1 for having a useful, active community which also frequently gives free games
+1 for having good customer support
+1 for offering frequent sales
+1 for having downloader and Galaxy for easy download/organization of games
+1 for almost always including extra goodies with games
+0 for nearly useless friend system
-0 for not being able to buy multiple games at once
-0 for having non-organizable wishlist system
-0 for not being able to delete certain people from chat so they're not still on your list
Overall score: 9/10
Humble Bundle:
+1 for having cheap games
+1 for including Steam keys
+1 for sometimes including Android games
+1 for having multiple platforms
+1 for having DRM-free games
+1 for option to donate money to charity and decide what portion of the money goes where
+1 for having very frequent change in bundles
+1 for not always selling games, sometimes movies, books, magazines, and developing tools
+1 for now having the option to pick your own charity
-0 for having no community, because they're really just a storefront and don't need it
+0 for lack of dowlnoader of any sort
-0 for bad game choices because these rotate in and out frequently, plus, this gives the opportunity for some otherwise-unknown indie developers to get themselves out there
Overall score:
10/10
Basically, Humble is better if you want to save money, while GOG is the more "upper-class" way to buy games. Even if you hate Steam keys, you can just keep what you want and ditch what you don't with Humble. Hate the company or the developers? Give to charity. Don't like the charity featured? Pick your own. It's a win-win any way you look at it.
This brings up an interesting point for me. How does Humble Bundle handle updates for these games and does it get updates the same time as Steam does for the titles?