I don't have prescription sunglasses, as I mostly wear contacts, but I wanted to share that for years, my Mom just used regular prescription glasses (not the transition kind) and battled with clip ons and the like. She finally got some really nice prescription sunglasses and they have been very useful. Mostly for driving, especially in the morning when the sun's coming up at just the right angle to be in your eyes, and the same on the way home from work - sun's going down, and you're fussing with the visors in the car and yadda yadda yadda .
After years of messing around with clip ons and/or regular (non prescription) sunglasses she finally decided to spend the money on a really nice pair of proper prescription sunglasses. I don't know the specific style, but I do know that the frames were Prada and that they look really stylish on her. She keeps them in her car at home, and carries them in her purse when on vacation to sunny climes. Living in the Pacific Northwest, you wouldn't think you'd need sunglasses all that often, and you don't really - but still, it's not very nice to have your eyes watering when the sun's glaring at you on your morning commute, and it's wonderful to have the option to wear the prescription sunglasses when the skies are bright - for instance, if it's sunny, Mom will take the sunglasses with her out of the car, if she's going to be running errands and the like.
Given her experience, I would absolutely recommend getting prescription sunglasses. If my contacts start becoming a problem and I have to wear glasses more often, I will get both the regular specs *and* the prescription sunglasses.
I have glasses, but I mostly just wear them around the house when I've just woken up ...before showering and getting ready for the day. The rest of the time, I'm wearing contacts, plus non-prescription sunnies when needed.