I suppose this depends on your age, how much you have set aside to spend on the procedure, and how much you intend to continue smiling the same way.
Some folks swear by Botox, but in the end it could be more expensive than waiting a bit longer and having a total face lift, because you have to keep going back for Botox injections.
I haven't heard much about dermal fillers, but I am skeptical about their appearance as aging continues to thin the skin. Instead of having laugh lines, you could end up with raised ridges where the filler has been injected.