I prefer the absorbant/adv coolant. For NF, it makes our LTs damn near unstoppable. Mediums die, enemy artillery dies (can survive the initial barrage which is generally what it takes), and of course AFVs are dying in droves. IF the enemy gets plasma though, it's generally a REALLY good idea to get biodiesel. It allows you to at LEAST try to run and save the res/tank if you're overheated. Or, damn the torpedoes and full speed ahead and go for hull damage.
Only repairs armor if there is any left. If a shot destroys the remaining amror on a side and some damage to the hull, regen wont activate. (at least, i think thats how it happens)