What is best type of paint to use on a cement block wall?

the right way to do it is apply blockfiller first, blockfiller is a thick acrilyc water based paint that can be applied by roller and brush. it fills all the cavity's so you can obtain a uniform appearance with the finish coat(s). then you just need to decide between flat,eggshell or semi-gloss finish.(assuming its an interior wall) flat hides defects best but is not washable. that can be bad if you have small children! eggshell has a little shine to it but is washable. (im a commercial painter and this is what we usually use in offices schools etc. where theres high traffic.) semi-gloss has the highest sheen and is washable but usually reserved for trim (doors, frames base etc.) as most people dont like glaring walls. for an exterior wall blockfill then you have the same choices to make just with exterior paint.all blockfiller is good for int. or ext.