More flex--

personally i think short has more flex although i ride a longer board

Well, really it depends both on the board in question, and the size of the board.  If you really want a soft board, you should buy a board that's specifically designed to be soft.  Having said that, if you buy an undersized board for your height/weight, it will perform a bit softer as you're basically overloading it's designed capacity.  Likewise an oversized board will perform as if it were a stiffer board.

Also, I suppose you could look at it as softer freestyle/park boards tend to come in smaller sizes.  While stiffer freeride boards tend to come longer.  This is mostly do the the preferences of people who ride those types of boards.

But really you're poll is looking at it wrong.  Birdy has it correct if you want soft, buy a soft board.