Sigur Ros is one of the few bands that I actually like everything they have put out...and just about equally at that.
If I had to pick a favorite I'd prob. have to go with Ágætis byrjun followed by () as a close second.
Their music is so fucking good though. I like putting it on at the end of a long work day and just chilling and relaxing to it.
They got a lot of shit coming out in the near future too. A EP in August. A live DVD in Oct (can't wait on this, their shows are fucking amazing, catch them live if you can.) and then also in Oct a full length acoustic album of songs from their previous albums. Plus they are working on songs for various movies and from what I understand a full orchestral piece which should be interesting.