Superman vs Goku

I have decided to start a "VS" series where I will match up certain comic book or anime characters and say who I think would win and why.  I figured why not start with the big dogs?  Superman vs Goku.  This battle is interesting because it really depends on when and where it takes place.  Let me explain.

Superman:  Superman is extremely powerful, everyone knows this.  The thing is, if he isn't on Earth (or by a yellow sun) his powers start to decrease until he eventually becomes an ordinary man.  He also tends to have trouble against other beings even close to his level because he spends so much time trying to tone himself down and not hurt anyone.  Because of this he also doesn't have that great of fighting ability and generally just stands there and lets people hit him.  Now of course all of this depends on what version of Superman we are talking about but I am going with what most people know of him from the moves and comic book.  He has shown the ability to fight though, like against Doomsday or Darkseid.  When he is pushed he seems to focus better and use his powers at a higher level.

Goku:  Goku's power level changes a lot over time.  He is constantly training and eventually learns how to take new forms, like Super Saiyan level 1, 2, 3 and 4.  The Goku from the first Episode of DBZ wouldn't last 1 second against the Goku from the last episode.  Because of this constant improvement from Goku it really just depends on what time period you are talking about with him.

In a head to head match up, Superman beats Goku if it's early on.  If the fight takes place after Goku reaches Super Saiyan things start to change.  If it takes place past SS1 Goku wins for sure.  Goku is the superior fighter and later on has enough power to destroy an entire planet, even Superman can't take that kind of power.  If this fight takes place anywhere but on Earth Goku also wins as Superman will be depowered until he becomes a regular man, whereas Goku's powers function the same anywhere.  I suppose you could call this one a draw since either one of them could win, again, depending on when and where it takes place.

These two characters are both big dogs and they both represent how their countries tend to do characters.  Superman was given his powers by birthright (and circumstances beyond his control like being sent to Earth).  He never really develops his powers much beyond what he had when he first discovered them.  Goku on the other hand worked really hard for most of his progress.  He is constantly training, fighting tougher villains, finding new training methods, etc to get stronger.  He was also born with certain abilities beyond ordinary men but nothing like Superman.  One power that Goku was born with that would help him against anyone is that he constantly improves every time he fights someone.  So if he fights someone who is close to the same power level as himself and loses, he will "evolve" to become stronger after he heals, meaning he should win the rematch (Doomsday has a similar ability).     

If anyone has any other match ups they would like covered let me know!