To be serious, unlike most of you... Use a pattern of smooth sandstone/regular sandstone, you can make it checkered, or 2x2 checkered, they look good together
Hard clay with patches of stained clay,melons and chiseled sandstone,maybe with the occasional emerald block.
Smooth sandstone, birch and spruce wood (and planks), throw in some glass, and maybe some stained clay. If you want to be eccentric, make it out of water.
I think that hardened clay should be worked in, but not everywhere. Using logs and planks as well as glowstone can make for some amazing floor designs. I can do one floor if you want, but it would have to be a rectangle the minimum dimensions would be a certain number. Quartz might be cool, but I wouldn't over do it.
Just don't do it out of quartz blocks. You'll regret it if you do, trust me. I'd say endstone, wool, clay maybe, wood, glass, etc... Cheap materials which you can have fun designing with, and they don't look as "bad" as dirt or cobble