What's a floor without a rug? And what's a classroom without a useful rug? Don't just get something cute! Get something you can use to help students learn!
I prefer round rugs so students can sit in a circle and all be spaced evenly from me.
I like rugs with separate areas or spots to determine where to sit.
I like rugs with info so I can play games, similar to Twister!, on them! Great for kinetic learning!