i wasn't really into At the drive- In, meaning i never heard a full album. But there were two or three songs from their last album i liked. About Mars Volta, i listened to their first album "Deloused sth..." and wasn't too much impressed. The music is technically impressive and that, but i somehow couldn't get into it. In some songs i couldn't stand the voice to be honest, and at points the music gopt a bit too twisted for my taste. Still if i would give it another try i dunno maybe i would get more into it. Many alternative music fans seem to be very enthusiastic about it.
Hmm, Claire, you should try Dredg btw, no emo or "post hardcore", but alternative anathema like, hehe.