Full album. EP's fun but at that point they were one of the hundreds of nu-metal bands out there at the moment. The full album's way more fleshed out.
While songs like And One are breathtaking on the EP, as a whole the full LP is far more consistent quality-wise.
The Hybrid Theory LP is a release that somehow defined the band. Linkin Park would be nothing without HT, let's be honest about it. It's also timeless. I voted for the EP anyway. Because I'm so hipster