How much do you want to spend? If you plan to visit the city, stay there. The airport is not so far away.
A nice hotel is the Lindner Main Plaza
http://www.lindner.de/en/MP/
On their Website the price is 84,-€ for 1 Person + Breakfast (I think it's quite expensive with 26,-€)
They have an airport shuttle for 25,-€
http://www.lindner.de/en/MP/120Direc...omplexdoc_view
Of course there are also all main hotel chains in town.