My fiancé recently purchased a BMW Z4 that came with a mesh wind deflector. He prefers the look of a plexiglass wind deflector better, but I'm concerned that it won't be as effective as the mesh deflector in keeping wind out of the cabin. Based on PERSONAL EXPERIENCE, which did you find to be more effective?

There's no doubt that the glass is a better deflector. Your also gonna get less noise that way. The mesh is designed to let a certain amount of air pass through, and that will increase your gas mileage but only very slightly. For the comfort and peace, go with the glass.