AA, UA all fly the 757 to MAN, DL flies the 767, and US flies the A330. MAN must be one of the only destinations in Europe where they are stronger than all the other carriers.
A quick look at the Summer '13 schedule
AA MAN-JFK 757 daily
AA MAN-ORD 757 daily
UA MAN-EWR 752 6 weekly
UA MAN-IAD daily
DL MAN-ATL 332 daily
US MAN-PHL 332 daily