I've found the P-38J (G and L too) to be rather effective in killing any bomber in this game. It has the fire power to kill a bomber in a single pass without needing to use a lot of ammunition and if you set up your attack angle correctly you can even take out the entire formation in a single pass.
Honestly, which is the better bomber killer is purely subjective in most cases. With the exception of a few fighters, the fighters in this game are all capable of easily dispatching bombers. It really boils down to skill and how you attack the bombers. Hell, I've shot down a Lancaster in a Stuka before.
ack-ack