I have an older (1920's) home I am rehabbing and plan to rent.  The porch has the old battleship grey paint its floor and it is chipping.  Does anyone know of a really good paint or paint/epoxy that is easy to apply and will be durable?  This is an upper scale rental so I want it to look nice.

The best paint is good floor prep. Sounds like the previous owner didn't do you any favors as it's chipping. 

I'd throw a pressure washer at it at a minimum. I'd probably hit it with a wire wheel on a grinder,  especially in the high traffic areas. 

Hello, Glidden from HD makes a decent porch & floor  satin latex paint. I use there steel gray color to paint my concrete boiler room floor. After nine months my floor is holding up well.  

@Sandy Uhlmann  is the porch exposed to the weather conditions? If so I would stay away from using Latex paints. As @Michael Herr  noted it's all about the prep work, that being said although it's not "easy" to work with oil base paint would last the longest and stand the test of time and weather conditions.

I suggest using a stain once the paint has been removed. Because paint will just peel again. 

Stain it 

stain/etching is the best solution in my opinion.

You have to remove chipped paint and sand the surface a little so the next layer of paint will stick. If you are painting it then use a primer like kilz.