Steam Sale: What should I buy?: Dust: An Elysian Tail or Garry's Mod
That's though, but I think you should by Dust.
Already beat the game on Tough on XBLA; don't feel like touching it ever again
Oh, well, then definitely buy Garry's Mod.
I'm already making games with my own assets; why would I use someone else's toolset and not make money off the result?
...well, why the fuck did you even ask then?
Dust is really great. Once I started playing it, I didn't stop till I had all the achievements.
Garry's Mod makes for good laughs if you're patient with it and have the right games.
EDIT: Wait, I just read your descriptions...why are you asking this question again? You don't want either. Don't waste your money. Get some lunch instead.
This edit will also create new pages on Giant Bomb for:Beware, you are proposing to add brand new pages to the wiki along with your edits. Make sure this is what you intended. This will likely increase the time it takes for your changes to go live.