Statutory / contractual periodic tenancy

Tax Planning and Financial

Is there a disadvantage to the landlord or tenant if the tenancy agreement is a statutory or contractual periodic tenancy agreement compared with a fixed term assured shorthold tenancy agreement? Is statutory or contractual preferable? (The fixed term contract is due to finish shortly &we are debating whether to do another fixed term or change to periodic as the same tenants are staying.) Are we, the landlord at a disadvantage if the tenants have a periodic tenancy agreement?
Also had great trouble accessing the RLA helpdesk. If I click on help desk - get asked for my membership number etc.. I complete this, get welcome message - offer to access help desk - click on this &get sent back to previous screen to enter my membership number - go around in circles. Rang RLA and was told to access the website to post a question. Spoke to RLA and was told to either email / post a question on the forum, but note the comment that the forum is not as good as the help desk. How do I access the helpdesk please?
Thanks