It really may not matter alot, depending on the load of oocycsts in your soil. Medicated (with coccidiostat) is no guarantee that they will not get cocci--trust me, I know. And if you are in a wet area or have a prolonged period of rainy weather, that makes it worse. I end up treating almost every batch of chicks that hits the ground here, even when they've been on medicated feed, so you can feed either, but watch for signs of their systems being overwhelmed by oocycsts in the soil and treat with Corid. It won't hurt adults to get some medicated feed, but starter is more expensive than other feeds, normally, and it will cost you more if they eat it all themselves.
The least likely to contract cocci here are the chicks with broody hens. Either they eat mama's poop and get antibodies from that or they are taught to eat things on the ground that prevent it, I'm just not sure. But my broody babies rarely have to be treated for cocci.