See the data sheet for the TIP127 for max power. You also need to refer to the safe operating area graph, which plots collector to emitter voltage against collector current. The graph is used to determine the operating conditions for the transistor with a given power supply and load, and may result in the need to derate, at the limits, the transistor you are using. It may also mean choosing a new transistor.
You have to design a heat sink for the operating conditions, so it is not possible to say which is most suited, power dissipation, max junction temp, thermal resistance from junction to case, case to heatsink, heatsink to air and max ambient temperature are the important parameters. If you use an insulating washer between the transistor case and the heatsink, the thermal resistance for that must also be included.
Heat sink design is not trivial, often assumptions are made, so design tends to be on the conservative side to be sure of a safe result. Where and how a heatsink is placed in or on the equipment plays a major role on how heat is dissipated.
Below are some typical links, and a youtube video that may help, and there is a lot more info on the web.
http://www.ti.com/lit/an/slva462/slva462.pdfhttp://www.digikey.com/en/pdf/w/wakefield-the...lutions/heat-sink-design-for-thermal-analysishttps://www.youtube.com/watch?v=8ruFVmxf0zsCheers,
Richard
