This should be based on purpose and use of your commercial vehicle. If the vehicle is not used much, or if you only plan to use it for a short period of time, then you can go for third-party coverage only, because it is compulsory to have. As a business all vehicles should be insured always at least with third-party commercial insurance.
But, if you wish to go for more coverage, including better long-term options, and more protections for your own vehicles opt for a comprehensive policy.