The OQF 17pdr was the most effective and efficient AT weapon mounted on any Western Allied vehicle.
Once again, the OQF 17pdr for artillery mount.
Aircraft would probably be the Vickers-S 40mm mount on the Hurricane IID. The Molins 6pdr on the Tse-Tse didn't have much capability against tanks while in flight, and was much more of an anti-shipping weapon.
It was called a Tse-Tse because it had more bite than a Mosquito. I don't recall a story of a Tse-Tse knocking down a Ju-88, I'm not up on Mosquito operations to be honest. Yes, the Molins took 6pdr shells. I don't know the precise shells that were used. It wasn't ever used for anti-tank work as far as I know. It was an anti-ship weapon, but did support the Normandy operations for a while. The Tse-Tse has one U-boat to it's credit, the 6pdr was effective against the conning tower on the U-boats but no better than rockets. It's low rate of fire makes it ineffective as an anti-tank weapon, it could be used and probably would destroy most armour if hit but the question of actually hitting in a hostile environment still remains. The Hurricane IIDs were ineffective in areas with high enemy concentration but achieved great success in the open areas of the North African desert against all soft and armoured vehicles. A Mosquito carrying two Vickers-S would be an interesting concept, I think ... but I suppose it would have been brought up at some point and thrown out. I certainly wouldn't like to be on the receiving end of a Hurricane IID even if I was in a Tiger.
and if you mount 40mms in a mossie you're either going to be able to fit more 40mms or carry more ammo, possibly bombs too which makes for a very interesting discussion, but for most of the war mossies were too scarce to be wasting on tank destroying when the now abundant hurricanes could do it, and i don't believe the Tse-Tse was ever used against tanks..........