The 4-8-4 type probably had the greatest variety of names.
Following is a list of names that different railroads used. It is pulled from memory from reading numerous books, but if there are corrections or additions, by all means, please add them.
Northern was for the most part a commonly accepted name on the following railroads:
Northern Pacific, Great Northern, Spokane, Portland & Seattle, Denver & Rio Grande Western, Chicago & Northwestern, Milwaukee Road, Union Pacific, Santa Fe, Missouri Pacific, Frisco, St. Louis Southwestern, Wabash, Rock Island, Chicago, Burlington & Quincy, Toledo, Peoria & Western, Soo Line, Grand Trunk Western (US), Delaware & Hudson and Reading.
New York Central called them Niagaras.
Lackawanna called them Poconos.
Lehigh Valley called them Wyomings.
Richmond, Fredericksburg & Potomoc called them Governors and Generals.
Chesapeake & Ohio called them Greenbriers.
Nashville, Chattanooga & St. Louis called them Dixies.
Southern Pacific called them Golden State.
Central of Georgia called them Big Apples.
Norfolk & Western called them Class J.
Atlantic Coast Line called them Class R.
Western Maryland called them Potomocs.
Canadian National called them Confederations.
Nacionales de Mexico called them Niagaras.
Some very large railroads never had a 4-8-4, including Boston & Maine, Pennsylvania, New Haven, Baltimore & Ohio, Pere Marquette, Louisville & Nashville, Southern, Clinchfield, Virginian, Florida East Coast, Seaboard Air Line and Illinois Central.