If i have data in excel and same amount of data in the database, then which would give better performance in transformer.
How much data are you talking about? If it's small enough to fit in excel, theres probably not a noticeable performance difference.
EXCEL without a doubt !
However, when you talk about this, this performance is about time taken to build the cube, not the the time taken to query the data from the cube !!
Why excel? I would have thought Database, since we could have used indexes while data retrieval
because Excel is a flat file so the data is read faster. Even if you have indexes in the DB, the DB still has other processes running when you try to retrieve the data and the DB is always in multi-user mode whereas Excel file is always in a single user mode.