hi..
See lord shiva is said as Mahadeva it means greatest deva but lord vishnu is said as DEVADEVAN means deva for all devas including the greatest deva...
And you people will know the place of siva is kailasam that is said as himalaya which is earth. but lord vishnu's place vaikundam and parkadal both of the place is not in earth it present behind lots & lots surya mandalam.. ok this shows lord vishnu is the supreme god