I painted mine with porch and patio floor paint and then put on rubber treads. I've got two young children and wanted to have something that was slip resistant. The rubber treads, from Menards for about $5/ea., are soft rubber and provide great traction with all types of shoes.
They are easy to keep clean, just vacuum up the debris and wipe clean with a cloth.
I thought about putting in some composite decking, but didn't want sand and junk falling in between and below. I use the space under the steps for shoe storage.