I have been researching this as well.

So far, the mesh are less expensive than solid and let the rain water go thru the cover, and supposedly last a little less time than the solid.

The solid covers are more expensive and you either have to pump the little bit of water that will stay on the top off, or buy a cover with the built in pump.

I am thinking I want a solid cover because that will keep the pool cleaner without rain water entering- but not sure if that is really an issue.