The best polish for oak furniture is correctly applied, traditional beeswax. It is relatively inexpensive as a little goes a long way, and can be easily bought on the internet or at bespoke hardware...
If the furniture is outside and exposed to the elements, it's not recommended that you oil the furniture as this will cause the growth of mold and discolorations of the teak. Using a true teak oil,...
Using products that are specifically for oak furniture is the best way to clean it. If you use something else, it could ruin the oak and no one wants that.