Start with the workflows you need to support. Document who uses the system, which tasks matter most, and what happens when a request fails. A feature list is useful only when it connects to those journeys.
Compare the boundaries of each product. Ask which capabilities exist today, which need customisation and which depend on an external provider. Request a walkthrough using representative scenarios rather than assuming every illustrated capability is included.
Review how data, roles and operational reporting will work. Then agree testing, deployment responsibilities, ownership and support arrangements. An explicit scope makes the choice easier to assess and the implementation easier to manage.