Most corporations or LLCs require some kind of annual fee and if you should ever dissolve the corporation you must pay the $200 tax to re-transfer the suppressor (or other NFA item). Trusts are usually free forever.
Just to clarify, if you dissolve a trust or transfer it to a new trust, it requires paying the $200 tax stamp fee. The main advantage of a trust is that it may require less paperwork filed annually and are less public than the corporation route. However, you must be careful about creating invalid trusts using Quicken or other form trusts.