Ok what's up with Rumplestilkson ?

I think that is one of the big questions of the show. For a while I thought that he was so evil that he made even Regina seem good. Now they seem to have turned that around, but they could very well turn it around several more times before the show is over. I think the safest bet right now is that he is on whichever side benefits him the most. Remeber though, that Regina has Belle locked away, which means that any alliance Regina forms with Mr.Gold can only be temporary.

Nobody (outside the cast and crew, of course), knows. Rumple, right now, is playing both sides of the fence, but it hasn't been revealed as to why.

He is on Emma's side...but not Mary M's or David's...and definitely not Regina's. Really, he's got his own agenda, but it mostly revolves around Emma.
Think about it. He made a deal with Regina, but he also agreed to help Ems. But in the end, Emma was the one who appears to have won. Because Gold helped, just like he helped her become sheriff.

First of all its RUMPELSTILTSKIN and he is more powerful than the queen herselfhe is also the KING OF DEALS

Rumple has only person's best interests at heart: himself. Deep down he couldn't care less about Regina or Emma. He's just using them both to get what he wants at a specific moment. If he wants something from Emma, he'll pretend to be her friend. If he wants something from Regina, he'll pretend to be her friend. That's why he keeps flopping back and forth between the two of them.