What is the best option to use for my horse Arti-Gold or Arti-Sport?

This depends on several factors: Arti-Gold is usually used as support after surgery, with foals and yearlings (0/X legs, growth plate inflammation…), maintenance of all horses and ponies and in case of mild crippling.
Arti-Sport is more commonly used to horses and ponies in competition.  It is dosed very high, just like the regular Arti-Gold, but with additional hyaluronic acid and anti-inflammatory herbs that are allowed. 
The regular Arti-Gold contains Harpagophytum (devils claw), which is mentioned on the FEI list.  Arti-Sport is adapted to the FEI standard.