Most of the websites we've all searched for racks and benches and such also sell "flooring" of different types and price ranges. I've also seen references on bodybuilding boards to stuff sold for barns and stables. Not sure if that's intended to provide a cushion for the livestock from the cement floor underneath or vice-versa, but those animals often outweigh what we put on barbells, and any flooring like that oughta be ok with moisture.
Epoxy is good since when the time comes that you either sell, or decide that you dont want a gym in the garage, it serves a purpose.
Tiles are nicer, but cost more. But you can pull up and re-use when you are done. I bought the thinner ones, I think 8mm. They are durable as all get out. You can deadlift right on them, drop weights...etc.
The tiles are a little more expensive per sqft, but they are super easy to lay and you dont have to worry about 'seaming' them or holding in place.
If you plan on keeping garage gym a while, I would use the tiles. And you can always move/sell them if you want at a later point.