The "Evil Empire" refers to American Mobile - which includes a whole bunch of other agencies. The empire refers to the dozens of other named agencies that are owned by them.
Some travelers have had problems with them (I am one of those) and it generally doesn't pay as well as some other companies. But quite a few big hospitals have "exclusive" contracts with them (only AMH travelers can work there - no other companies).
CrossCountry is also a large conglomerate with many exclusive contracts, but they did better by my...and the exclusive contract hospitals for me were in better hospitals.