Steam

cs source isnt as good as the original imo but team fortress 2 blows all away
 
I already have Counter-Strike and it seems a bit odd to buy the game again just for a Source version....
And my laptop most-likely doesn't have a good enough graphics card to run HL2-based games like TFC2.
It's got 2gigs of ram and a dual processor, one 1.66 and one 66, but it runs Doom3 quite choppy... so no...