I don't think there is such thing as the "best" fuel gun. Kyosho use to make one that was pretty good and leaked very little. I think RB has one as well as Xceed. Proline and Losi also have fuel guns on the market. The Kyosho and RB are all metal while the Proline, Losi, and I believe the Xceed are plastic housings with metal inner tubing. There are probably other guns out there, but these are the ones that I know of. Hope this helps in your search.
It's not what you know; it's what you can prove.
The only thing that is for sure is that nothing is for sure!!!
The needs of the many outweigh the needs of the few, or the one.
There are 2 things in life that are infinite: the universe and stupidity.