The smartest choice would be what's recommended by the manufacture; which will be the "only" right answer.
You also need a breaker the 'trip curve' of which handles compressor [motor] loads, otherwise you might need a 'soft start' kit.
On the side of every unit is a "Minimum circuit ampacity" and a "Maximum fuse or breaker size". You size the wire to the former and the breaker to the latter. DO NOT guess at this. BTU ratings are irrelevant.