I think that the shortest answer is, ‘it depends’ but a better answer would be, ‘whichever you’re most familiar with.’
ERP is not a business model - its purpose is to constantly reflect the business and its requirements. Effectively, it’s all about change.
Talking of requirements, you don’t seem to have any! Having mentioned Agile, you’d surely want a set of requirements to break down into sprints/iterations.
Also, and I’ve done it myself, it is possible to agree a set of user-requirements and acceptance-tests, at the same time. The benefit is that UAT of this sort helps to manage newly-realised and changed requirements, in relation to the project’s resources (time/money).