What is a good car? What is a good woman? What is a good man? You have asked a very vague question, so you need to refine the parameters.
It is important to find one that suits your wants and needs. Pulsar, FLIR/Armasight, Trijicon all make good thermal gear. So the question is more about what you want/need and finding a scope to match that given your budget.
How far do you normally shoot critters?
What are the longest shots you take?
What are the longest shots you would like to take?
What type of critters are you hunting?
What is your budget?
What sort of rifle do you want this scope to be on?