Sebi, if I had to choose one of your two options, I would go with #1. Specifically, the pipe-delimited version, since it would make it a little easier to create/alter import files in text editors. I think the two options have separate use cases, however.
Option 1 is good for people who have their own XLS or CSV tracking files, or people who are also using a desktop app with an export feature.
Option 2 would be good for something that I do, which is import Starter Packs (like the new Scars precons). I just go out to Cardkingdom or something, copy the decklist, and paste it into the text box. If the dropdown existed, I wouldn't have to take the extra step of going into a text editor and replacing paragraph breaks with paragraph break, pipe, 'Scars of Mirrodin'.