Quoted from Frax:

Frosted - If the bulb is visible from player perspective it helps to tone it down. Frankly, I buy *all* frosted and then pop off the tops if I want to use them for inserts.
Flat vs. Rounded - Rounded will have less light thrown to the side and more towards the tip of the lamp. Again...frosted is the way to go IMO, and if you pop the white cap off...guess what...you've got a flat head SMD LED now.
Faceted vs. Smooth - I can't really think of a single reason to pay the premium for the faceted ones. The point is again, it changes the directions the light travels and faceted are supposed to be a more even coverage out the sides. I don't personally buy it, I've owned the faceted ones with round tops from mulitple companies..I'd rather just have...wait for it....frosted.