Portal 2 was harder because there were those long stages where you hop around on the catwalks trying to figure out where to place your next portal.
Portal 1 was harder in the sense that there were more full-fledged puzzles to complete back-to-back.
Portal 2 was easier: You just look around for the one spot you can place a portal.
Portal 1 tended to have lots of space to place them.
Also, beat it within the first 24 hours of it being out.
