It may not be a unanimous decision but for years the consensus has been Kroil is the best.........although transmission fluid mixed with diesel fuel is darn good. There have been "experiments" post here before and Kroil wins by a smidgen!
Search "kroil" and you'll probably find an hours worth of reading.
I stocked up on Kroil when I would get buy one of the big cans and get one free....sometimes even free shipping...and as Jerry suggest, buy it in the gallon cans its much more economical and use your own spray bottle. If my stash of cans ever run out that's what I'll do. I like Kroil and the plants where I worked for years use it as their #1 got to can.