What is the best liquid bathtub cleaner?

I actually have a tool that almost eliminates the need for bending over the tub. Kind of like a sponge mop, it has a thick, square sponge at the end of an extended handle. It easily reaches the whole tub and conforms to the rounded corners. It's easy to rinse out as you simply stick it under the faucet and squeeze it several times until clean. If you don't have one of those tools, you will have to use a larger household sponge, bend over and do it the old fashioned way. After going over the surface completely, rinse thoroughly and check for stubborn areas.