PC Best Source game ever? Let's hear it.

Okay let's hear it folks, a lot of people think the source engine is pretty outdated but I must admit I love it and I see many other engines try to replicate some of its feeling & its features.

What do you think the best Source engine game ever was? Half Life 2? Counter Strike Sourc? Source mods like GMOD, Synergy, Zombie Panic!: Source, etc. are welcome.

I'f I'm talking valve games only, and no mods, My vote is for Portal. One of the best games ever.


otherwise I love GMOD.