It depends on how much you use it. I change my mesh and wool every two to three weeks depending how much I use it. Mesh wicks, IMO, is good for genesis type tanks. Cotton is great for micro drip RDA/RBA's (tried cotton, but it burns to fast for my liking), But I still like the eko-wool in my drip atoms and mesh in my genesis style tanks.
It also depends on what you perfer in vaping wises. I like huge clouds when I vape. You might want flavor, vape and the hit......So, if you are looking for that kind of vape, then I would do a genesis type tank, with a 3mm eko wool sleeve over a 2.5mm ss mesh with a 1.5-2.0mm bigger hole in the genesis style top.