Sempiternal and their previous album are pretty great. The first two albums aren't that great, they sound too rough and cacophonous. I don't have a favorite song, though. I like all songs equally.
I'm definitely more of a casual fan, so if my answers are a mainstream, bear with me. I think my favorite song is Sleepwalking or House of Wolves. My favorite member is Ollie? I guess?
I love the newest album, That's the Spirit. Although I haven't heard much of the previous albums, they would probably be too harsh for me, my brother says. I like Follow You and Oh No, followed by Drown.