It's more of a people & process question, rather than there being a right or wrong approach.
For example, if there is a team of content editors that can also handle the personalisation activities then it's probably an easier workflow to do everything within AEM; however, there is some additional functionality available in Target that isn't available in AEM personalisation, so if there is a local/centralised team (or SME) responsible for Target activities then it might make more sense to use that workflow.