What's the best filler that last longer for deep static frown lines between eyebrows?

You can never go wrong starting with a neurotoxin like Botox in the glabella forehead lines.  If the deep furrow remains after Botox injections then there are a number of fillers available which will finish the job quite nicely.  Not a huge fan of permanent fillers in this area.  See if you can get a 1/2 cc syringe as you will not need very much filler to manage this area.

As someone has already mentioned this is a rather tricky area to treat. Those static lines you are seeing are also the location of the blood vessels that supply blood to the forehead. These are very small thin vessels. This is also an area that the tissue is not very thick. The risk is that you can compress the blood vessels with a dermal filler or even get dermal filler in the blood vessel. This is the primary reason everyone is saying to use a neuromodulator like BoTox  to decrease the muscle activity in the area. The other reason is if you do use a dermal filler and don't use a neuromodulator , the increased muscle activity tends to cause the dermal filer to migrate or resorb faster. As you can guess a combination treatment tends to me more effective. Also keep in mind if you use a dermal filler in this area, you want one that is easy reversible. If you do have a complication you want to easily be able to dissolve  the filler.
What you will find in using a neuromodulator  with deep static lines it will take forever to make them go away. It will soften them but the tissue is damaged in this area . This is why many will suggest skin resurfacing in one form or another after you treat with a neuromodulator . Which technique you use will be dependent on how much you want to spend and how fast you want to see results. This was a technique I often used and then would go back and treat with dermal filler later. In this way I would be treating a fine line and not a deep line. This is a much safer technique as you don't have to use a filler with a lot of body and you can also inject it more superficial. Less chance of compressing a vessel. The problem with this technique is it takes time.
A faster technique is to use a neuromodulator and then have smooth PDO threads placed in the area. This rules out the vascular compression or occlusion issues . Keep in mind you most likely will need to have the threads placed every 4-6 weeks until you are happy with the results. ( Often 5 times) and then once a quarter for maintenance . The PDO threads build up your own  collagen in the area .