You can actually get lime only concrete without cement in it. Cement is just the crap that builders started using at the turn of the century to get things to cure faster. It also removes the self healing ability that lime mortar used to possess back in the day. Not that that matters but while we're being particular
. I'd personally go with a smooth finished concrete. At least that way if you were to scoot a painted part over the surface it wouldn't take it down to bare metal immediately like a broom finish would. Also easier to scrub grease and other crap off and it's more durable than other surfaces.