why not just stick with the concrete floor ? (unless it's buggered)
to me putting anything on top of it just makes one more thing that needs maintenance, or cleaning, or you to look after it
dropped an engine on your concrete floor? no one cares
split dirty old engine oil on your concrete floor ? toss some cardboard on top of it and go for a cup of tea
come home drunk, wife's kicked you out the house, slept on the garage floor and shat yourself in the night ? hose it off and no-one will know!