Carpet or hardwood floor?

Hardwood floors if you have tapestry's or large curtains everywhere. Otherwise, rugs with drywall or panelling is fine.

I'd recommend a carpet. If it makes your room too dead, remove something else and keep the carpet. Floor bounce is generally problem #1 in speaker-room interaction. Minimizing it is never a bad thing.

I have found carpet to give better acoustics, but I don't particularly like carpet (for many reasons, amongsts which we have pets), so a good trade off may be rugs.

I love hardwood floors but unfortunately carpet sounds a lot better. I've tried rugs but a fully carpeted room just sounds better in my opinion. You get significantly more floor refections with a rug and hardwood floors.

I've got wall to wall carpet plus underpad, and I've received a lot of compliments on how my system sounds. I've made ZERO effort on room treatments to this point...so I'd recommend a carpet.