If we are talking in terms of most DANGEROUS towards humans in 'Home Aquaria', I would rank them like this. I would also be interested to see what type of bite a 5-6 foot 'Synbranchus Marmoratus' aka marbled swamp eel, would have upon a human? I heard they are very similiar to green wolf eels.
5) Stingray Sting/Venom
4) 5ft Electric Eel Zap
3) Giant Channa Sp. Attack
2)16" Fahaka Puffer Bite
1) 30"+ Mbu Puffer Bite
Some people forget to take into consideration the massive size of Mbu Puffers. They are designed to destroy hard-shelled crustacea. 6" Crayfish are like french fries to these guys. Taking off a person finger off at the knuckle is no exaggeration, as I have seen pictures. If a Mbu owner was careless enough to take his eye off even the most 'gentle of giants', it could possibly do some very permenant damage. A fahaka, especially with its own personal anger issues, is no whimp either..
Hasta,
Miles