Both movies are amazing.
I think that if you had to choose between one, though, Like a Lion would be the sure choice. It documents one of freestyle skiing's legends, and navigates through his life from the top to the bottom, from X-Games gold to drug addiction. This movie is sort of a one-time deal. There's never going to be another movie like it, whereas I can bet that Level 1's movie next year is going to be along the same lines as Eye Trip.
I'm not trying to bash Eye Trip at all, in fact I thought it was the best "ski porn" movie of the year. Just I think that the story about what Tanner has done for this sport is necessary to watch.
Anyway, they're both on iTunes (Like a Lion on Nov. 23rd) for less than $10, so I'd recommend seeing both.