Above: While these shots aren't perfectly lined up, Portal is another game that suffers from Xbox 360's slightly grubby colours. Peer at the character in each shot and you'll also notice that the textures on PC are noticably smoother - something that also comes across in Xbox 360's version of Half-Life 2.
Overall, then, PC takes the lead in the visuals department. But, then, our PC (an Alienware) does cost more than three Xbox 360's. That said, Valve has managed to bring Half-Life 2's engaging atmosphere to consoles, if you can overlook the odd grubby colour or smudged texture.
Once again, hit the gallery for full sized versions of several looks at Portal.