When you buy eggs, if you can buy the ones in cardboard cartons, go for it. Not only are they more easily recycled, but they break down faster in a landfill if (for some reason) you don't recycle it.
In my neck of the woods, though, the eggs in cardboard cartons are several dollars more expensive than those in foam cartons. So I buy the foam ones, but reuse them by giving them to my mom, who happens to have chickens. If you know a farmer with chickens (or can find one), they might appreciate the used cartons to hold their excess eggs. You might could even work out a trade. Five egg cartons for a dozen eggs, anyone?