One or two? I remember reading here on HN that one (or both?) of them is great. I never got to play them myself.

I was debating whether to specify which one, but then decided I would leave ambiguous.

Frankly, they're both great. I think I have more of an affinity to Portal 1, not because it's "better", but because it was first. That was a very distinct moment in my memory when the game mechanics "click" at the beginning, and you realize what's going on and there's no other game world like it.