Super Soaker flamethrowers suck. Or, at least when I tried to make one. Most people use gasoline, but that made me a bit wary.
If you can get a good pilot light, kerosene is by far the best thing I've ever used, though it's hard to get it to light at times. Has got to be the least flammable flammable liquid I've ever used
For those curious with my success:
http://www.youtube.com/watch?v=5lhOGFd4RTM
First one was better, but removed due to somebody flagging it as a terms of use violation. Takes a short time to get into it, was shooting out rust-kerosene mix for the first few sprays.