It's a quite obvious choice - Qlik Sense. Because of the following reasons:
Most of the existing things could be directly migrated from qv to qs, data model, objects (some needs to be re-worked), qvds
License migration is available from qv to qs, that is, you don't have to invest mucn afresh
Your development team is available already for qs (mostly people know qv; know qs), whereas - for tableau you might need a different set of people to be hired for this migration
