L investigated Kira and got it right but died before he proved it. Lunge investigated Johann and got it wrong but after a time realized his mistake and was useful in bringing Johann down and lived to tell the tale. However if I had to say who the better investigator is, I would say L soley because he is more open to the fact that he makes errors and Lunge wasn't open to this until near the end. Also L had superior resources. In strict intelligence I'd say they are near even.