A good rule of thumb is how much food you would get from eating it = more power given. The energy given depends on what you put in it. Bio is the easiest to get power from, just about anything can be put in it for power (if you can grow/breed it around/in your base you can use it for power, also poop from the seatreaders). Nuke gives the most power but the rods can be a pain to find the items for if you run out. a heat vent, they don't do squat otherwise).
Thermal is good if you have somewhere to put it (i.e.
