Select an epoxy paint for the strongest finish on a floor. Epoxy finishes are industrial strength and hold up well to spills, wear and corrosion. The drawback to using epoxy is that the fumes are quite strong, and a mild acid bath is sometimes needed to prep the concrete. This is unsuitable for an interior with low ventilation, but could be acceptable for an interior garage or other room that could be opened to fresh air.
Select a latex-based paint for a paint with the least off-gassing. Latex will not be as strong as epoxy or oil, and it will be more susceptible to wear. However, the volatile organic compounds are lower, which makes it better for interiors with less air flow. You also will have access to a more complete color line. Latex-based concrete paints are suitable for walls or blocks, and the drying time is fast.
Use an oil-based concrete paint for a compromise. It has more fumes than latex; however, it provides a tougher veneer. The color options will be more abundant than those colors offered in epoxy kits, though they may be more limited than the color lines for latex paints.
Pick mid-tone colors to hide stains. Battleship gray works well, but is dull. An earth color like milk chocolate is in the middle of the value scale and hides well without looking too industrial.