What is best filler for furrow between eyes?

Hello Diamondhank, Thanks for asking this question. This is a very common problem. The cause of the deep furrows in between your eyes are the contraction of the muscle under the skin causing the skin to wrinkle. If you relax the muscle , the deep lines will improve. There are instances when the lines have gotten too deep that you will need a filler . 
I use a very thin filler like Belotero for the deep frown lines.  You have to make sure to get  an expert injector as injecting the area carry certain risks. There are blood vessels underneath the forehead lines and if the filler was placed in the wrong area and too much filler was used, there could be a resulting ischemia ( blood vessels supply is cut off by compression). If there is ischemia, the skin can also be affected causing necrosis. Another rare side effect is injecting the blood vessels supplying the eye causing vision loss .These are rare side effects and can be prevented by going to an expert trusted injector.  For horizontal forehead lines, if these are superficial , microneedling, chemical peels or laser treatment  may help with these lines if Botox does not work. I also advise my patients to use Retinoids  ( Retin A products) as part of their daily routine to help with fine lines and wrinkles. Thank you for your question.
Best, 
Ladie Arana-Domondon, MD FACP

Sorry to hear about your prior experience. Neuromodulators like Botox and Dysport are the best treatment, in my opinion, for frown lines. I recommend you schedule an in person consultation with an experienced aesthetic physician to discuss your concerns and to come up with an appropriate treatment plan.