I own Street Fighter 4 & I'm thinking about buying the updated versions. I'm not sure if I should just Ultra Street Fighter 4 because its the most recent or buy Super Street Fighter 4 and play it for what it is or maybe the Arcade Edition. So which one should I buy Super, Super Arcade Edition, Ultra or buy them all?

the one that has complete movelists in the instruction manual

General rule of thumb with fighting games is just buy the most recent version. That's the one most people will actually be playing and (assuming it's not broken somehow) will continue to play.

Usually like this!

Unless it's another iteration of the series since they would be different games.

Buy Ultra, it basically has everything Super and AE have anyway thanks to the fact you can choose between different iterations of characters. (Though I really did like Super Street Fighter IV)

Buy a used Super Street Fighter 4 disc and buy the Ultra SF4 DLC. That will be the cheapest way into the current SF4.