Deks Olje or Sikens. Deks is an Oil of which you have a No1 and No3. For outside, you start with the 1 and keeps applying till the teak takes no more. Then you finish with No2.
Sikens is more a coating than an oil. Also best used the same way for outside use, by applying the base and then the top.
Both offer the best protection anything is going to give you outside. Deks will last 6 months, then wash and recoat. No sanding. Sikens will give much longer. The more coats, the better protection. You should get two years, then wash and recoat, no saning.
Any forms of clear Varnishes will look great, but require constant recoating and that means sanding down and starting again. 2 pot clear will give you 2 yrs.