Smith's weigh quite a bit more and clarity isn't even close...Costa's are great but Smith Action Optics fishing glasses are hi-tech glass as well. Glass is not only scratch resistant but there is far less distortion than with even high quality CR39 type plastic lenses...polycarbonate is barely optical material but is the lightest. Chose between the Smith and Costa product based on frame style and tint...they are both first rate and worth every penny.
If you want overall quality control... Action Optics aka Smith Optics... Makes all their glass lenses in their own labs... Costa only makes their own frames and outsources the lenses from a separate company... Also I don't think Costa offers PolyChromic Polarization which means the level of tint on the lenses changes depending on the current conditions... I've own a couple pairs of Smiths(non-glass) and their polycarbonate is pretty dang scratch resistant... I'd imagine their glass is even better