I developed a neighborhood where we used stained concrete as the finish floors in the homes. (Integrally stained, polished smooth in first day after pour, then scored in 3' squares on the diagonal. Beautiful--people thought it was a kind of Mexican tile.)
There are two ways to stain concrete. The pigment can be mixed right into the concrete in the truck (integrally stained). This is the way we did it in the homes. I highly recommend this. Even if something chips the concrete, you have color all the way through and it hardly shows. The color is rich. My floor looked like leather.
For floors that are already down, acid-etch stain is what is used. I used this in the community building for that neighborhood. The color isn't as dense, in my experience, as with integrally colored. The prior poster said to acid wash the floors--for floors that aren't new concrete--and then stain them. New concrete doesn't necessarily need the acid wash. Make sure you use an acid etch stain meant for concrete. This sort of stain interacts with the alkaline in the concrete and really stains it. It's not a pigment on top situation, where traffic will wear off the color. You may need to apply the product more than once to get the density/richness of color you want.
Acid etch stained concrete can be seen often in commercial situations. We've got a Whole Foods Market nearby that took an old A & P, the original floor, and stained it. It's held up great to a lot of traffic. The colors that are easiest and least expensive to achieve are in the red/clay color range.
Topping it off--I've had some people use special polyurethane and like it. I've also seen polyurethne start separating from the concrete, especially where there is an impact, then it chips away. But in other spots, it stays really bonded, creating an awful mess that just needs to be ground off to start again. In my own home, I used an acrylic wax that could be topped easily (water based), and could also be easily stripped. In a garage, I'd be tempted to just stain it and leave it alone. Butcher's wax can also be used, but that's more of a maintenance item, I would think.
Sorry for a long post. I haven't used any of the epoxy systems, but thought I'd throw my experience with stained concrete into the pot .
