Some of the key factors that should affect your choice of organisational structure include:
Simplicity – some organisations are informal, whilst others require registration and regulation.
Cost – although a few structures involve the payment of an application fee, preparation of all of the required documentation can (for some) become a drain on resources.
Speed – some structures can be created overnight, others may take months to become operational.
Privacy – only a limited number of structures can be kept completely private (subject always to any tax obligations) whilst others require regular publication of reports and accounts.
Profits – some structures allow for the distribution of an organisation’s profits to its members, whilst others are obliged to retain their profits (or surpluses) for future use.
Extract from How to Run a Charity, published by ICSA, focusing on the legal aspect.