I've had both Restylane and Juvederm lip injections and was very please with both procedures. I didn't realize how much volume my lips had lost with age until looking at old photographs. I did not want huge, unnatural appearing lips and my dermatologist injected enough to restore my former fullness, which left me with a much more youthful appearance. While I found Juviderm to last much longer in the areas around my mouth (over a year) it did not last any longer in the lip area than did Restlane. I haven't had either in a few years but plan to indulge myself again soon.
I do recommend doing your research and find a skilled MD that specializes in cosmetic procedures. A friend recently went to a spa to have dermal fillers in her lips and she came out looking like she had grown a duck's beak.