Viral was mildly amusing, what with losing every fight and stuff.
Rossiu annoys me because pre-timeskip, he's like "Hey, Kamina is right. If I put some spirit, it will move", and being pilot of the Gurren every now and then.
Post-timeskip, he acts like a jerk and seems to completely forget about Spiral energy - "A machine that runs on people's hopes? What have I been doing?!"