Neurotoxins like botox, xeomin, and dysport are really the best way to improve the appearance of the deep furrows that appear between the eyebrows. While some people have tried fillers in the past, I would not recommend this treatment because there have been many reported cases of skin necrosis and blindness because of improper injection into blood vessels in this highly vascularized area. Depending on the appearance of the rest of your face, forehead lifting may be another option to help improve the condition. Good luck!
I would say that Botox is the best treatment for improving the 11's between the eyes. If there is a deep furrow in the 11's, sometimes a filler (in place of or in addition to Botox) can be used to help. There are a variety of fillers that potentially can be used.