For whatever type the employer operates. Could be as trivial as C525 (thousands of them all over the world, multiple training providers with competitive course prices) or as exotic as G150 (just a handful of aircraft built and only one training provider, charging an arm and a leg). There's no universal truth and sometimes jobs on more "exotic" types come in greater numbers than jobs on "mainstream" types. Oh, and there are also corporate jobs requiring a B737 or A320 type rating.