I have two pairs of Tifosi transition lenses: Gavia and Envy. The Envy are my favorites in that they transition from nearly clear to smoke. They're great for days where you're going in and out of shaded areas and they transition fairly quickly.

The Gavia's range is much more limited and are good for days where the light is mostly bright sun. While the Envy doesn't block out quite as much light at its darkest, I've never felt like I wasn't getting enough protection. They're comfy, too. I've never liked hassling with changeable lenses, so the Envy were the best option for me.

Both are available at TE.