What kind of organism currently have the best immune system? human??

I presume you refer to higher organisms. Though I do not have an exact answer, I would suggest you look up the Komodo dragon. Contained within its saliva, as well as on its skin are bacteria which are lethal to other organisms. However, this bacteria has absolutely no ill effects on the Komodo.

 

http://en.wikipedia.org/wiki/Komodo_dragon

 

Komodo dragons also possess virulent bacteria in their saliva, of which more than 28 Gram-negative and 29 Gram-positive strains have been isolated.[22] These bacteria cause septicemia in their victim; if an initial bite does not kill the prey animal and it escapes, it will commonly succumb within a week to the resulting infection. The deadliest bacteria in Komodo dragon saliva appears to be a very deadly strain of Pasteurella multocida, from studies performed with lab mice.[23] Because the Komodo dragon appears immune to its own microbes, much research has been done searching for the antibacterial molecule in the hopes of human medicinal use