Wich is the most efficient/easy way for end-user to get data from Analysis database?
You can put your cube formula in a separate cell and reference the cell where users type in the name they want.  For example, if you have users put the branch name in cell B2, you can put this formula in another cell. 

=cubemember("Connection","[DimBranch].[Name].[All].[" &amp; B2 &amp; "])"