Dunno. You can't really compare them. I mean, yes, they are powerful beings and all... but they work at different levels. For example, take Seiya from Saint Seiya, Cloud Strife and Death of the Endless... there's no way to tell who's more powerful, because their standards are different.
If I had to decide based on sheer power, I'd say Goku, just because his powers are more "magic-like" than Superman's. At least, they involve projecting "vital energy" from oneself and all that. Superman is weak against that kind of "non-physical" power. On the other hand, if I were to choose based on coolness factor, I'd pick Batman.