They both have their advantages and disadvantages.

With mesh, the water flows right through but with it, so does some dirt. But, you do avoid having to pump off the top of the cover if you get a lot of rain or snow in the winter. On the other hand, since it isn't solid and you do get sunlight into the water, you sometimes have to deal with algae moreso that with a solid cover which blocks the sunlight.

Solid covers do keep the water cleaner but you occasionally may have to use a submersible pump to pump off the cover. Plus, decaying leaves on top seem to most always end up in the clean pool when you remove the cover in the spring. You also will probably want to use some type of air pillows or large inner tubes to keep water from puddling in the middle of the cover putting stress on the pool walls.

For the past several years, I have not used a cover. I keep after the leaves in the fall as I also have trees around my pool. (My Polaris 65 is good for getting leaves out of the pool.) But, then, once the leaves have all fallen from the trees, that's it. The water stays clear all winter. I do have a little dirt on the bottom in the spring but that is easily vacuumed up. (My Wanda the Whale vac is better for dirt.) I got tired of fooling with that huge cover and cleaning it upon opening was also a pain.