Subsidiary are considered as a separate legal entity even though it is owned by the parent company, will not be exposed to any liabilities from the parent company.
Branch as it is considered as another operating of the operating company would be exposed to any liabilities rising from the parent company, hence a subsidiary is advantageous for controlling tax and liability issues.
There are different tax implications on tax structures of Branches and Subsidiary, but since in the UAE there is no corporate tax or any on dividends/profits this does not effect the structure here. However the parent company can offset the tax paid in the home country if its branch in the UAE has suffered a loss, thereby reducing the overall tax paid.
For a branch, the parent companies financials must be disclosed to the authorities in UAE, in case of a subsidiary this is not required.
A branch would be considered as a non resident company hence it would not be able take advantage of the Double Taxation treaty UAE has with other countries.