Kintaro and Motaro were the best.. Goro looked like he was made out of playdo and Moloch doesn't really do much he just swings that ball over and over again.

Motaro was the easiest boss EVER. All you had to do was crouch and wait for him to approach before you uppercut.
Goro was quite cool, I thought especially in MK4.
Moloch is okay, although I find him to be a huge pain in the ass sometimes.
My fave though has to be Kintaro, his stance was cool and he was the hardest of them all.

I found that if you got Kintaro in the corner and kept doing low punch repeatedly you could finish him off!! :). Other than that, freezing then uppercut worked well with a few fly kicks in for good measure. I think that Motaro was the hardest to beat but I never tried that crouching technique, must give it a go sometime. Moloch isn't to hard if you use a fast character. Goro in MK1 was just fly kick mania. Jump back, jump forward and fly kick, jump back, jump forward and fly kick and so on. Goro from MK4 was pretty tough but the lightning bolt worked well against him.

Damn, I though MK4 Goro was also easy!
Because you could combo him like any normal character, I just ran the hell up to him, beat the sh** out of him and run up, throw him (which I must ask, why the hell can you do?) and repeat the process, and trust me the crouching thing works wonders for Motaro.