Best way to achieve - Data Sync between SQL Azure and Multiple On-Premises SQL server Databases

Best way to achieve - Data Sync between SQL Azure and Multiple On-Premises
SQL server Databases

I have a scenario as explained below and I need to implement the best Data
Sync method.
1.I have a centralized SQL Azure database(master Database)
2.There are about 20(this will increase in future) on-premises sql server
Databases.These database are not necessarily always connected to internet.
3.All master and on-premises DB's will have the same schema/table structures.
4.I would like to do bidirectional data sync between all on-premises DB's
with SQL Azure and vice-versa.
5.Data Sync frequency will be once in a day.
6.Each on-premises DB size is reasonable(not too big and not too small).
These below options I have explored: Different Options:
1 .SQL Azure Data Sync
2. Microsoft Sync Framework
3. SQL Server 2008 Change Data Capture
4. SQL Server Change Tracking
I would like to know the best possible method to achieve this.Please do
suggest me the best methods.
Thanks in Advance.