For sure, the largest pipe organ in the world is in the auditorium of the Atlantic City Convention Hall, but much of it doesn't work and it is just a few pipes larger than the Wanamaker organ at Philadelphia's Lord & Taylor Department Store. The largest church organ is at First Congregational Church, Los Angeles. The organ in the Cadet Chapel, West Point, New York, is just a few ranks smaller. Europe's largest organ is at Passau Cathedral in Germany. In Passau, it is regarded as the world's largest church organ because its owners define "church" as a space consecrated by a bishop. The world's oldest organ is generally agreed to be the one built in 1390 at Sion, Switzerland, and certainly unique is the organ built of bamboo pipes in the Phillipines. Another unique organ is that built 1925-31 by German organ theorist Hans Henny Jahnn to have stops arranged in masculine and feminine groups which are accessible by combinations only.
The world's largest organs, oldest organs, and unique organs are often described as such by their owners.
Here are some recordings of them and some books about them.