Janus:

Ripple foam is designed for dry flies. The theory being if you are REAL careful and jab your dries just right; the hackle will end up at the low spot on the ripple and not get mashed. While it ain't perfect it does work better for dries. Slotted foam is probably better than ripple foam for dries although the only outfit I know that sells it in sheets is Wheatley.

When I say slotted I am NOT talking about micro slit foam like you find in C & F boxes but rather the flat foam with a large slot or opening cut out of it to protect hackles.

I only use ripple foam on my drying patch because no matter how hard you try you will mash hackles. I prefer to keep dry flies in compartments.

Flat foam is good for everything else all the way down to size 32's.

Use what works best for you!