The great thing about Minecraft is I don't have to pick just one. And probably I can't just pick one. I can maybe pick a favorite combo, or a favorite type of wood block, but my bestest ever in the game pick? Uh, hrm, um.
Spruce logs? I had a little chuckle when someone offered to take spruce off my hands, which they could have if they'd come and harvested the trees. But let's be real, considering that I DO like spruce, if I chops it down, I keeps it.
Otherwise my combo of choice would be quartz blocks and sea lanterns. Long long ago I made a "clean room" in the nether with those, and it took an otherwise drab and depressing environment and made it look rather dashing. Dashing? That's not the right word, but I think you'll know what I'm trying to say. Or maybe creepy, like the opening part of a horror movie where the unscrupulous scientists take things a little too far and create a monster/portal into hell and naturally demons come out and just murder everything messily. But it looked darn good in its pristine condition, I tell you!