Hi Rupali,
For backup/restore method, you have to convert your target single DB to MDC before recovery because the topology information is not compatible between single tenant database and the tenant of a multitenant database mentioned in note 2141670 - Backup & Restore from a single tenant database into one tenant of a multitenant database fails.
For export/import method, it uses the pure data which is independent of DBs and platforms.
Regarding to which method preferred, depend on you.
Because that you may need to do something at SAP application level (for example, reinstall application server during migration), using SWPM for recovery is suggested.
Regards,
Ning