It's a subjective question. There will be no overwhelming response for any of the models released.
Local VoiceControl without the need to use Siri is a big deal for me (only the iPhone 4 has it; although, you can put back with jailbreaking). Retina display is still great; have changed the battery for a brand new one two months ago, so I still have all day battery life - and the speed is more than decent for me even though it's jailbroken and FULL of fun stuff.
I'm on the bubble, as it would be between the original and the 4. However, there are a number of things that make this poll vague.
Without a doubt, the iphone 4. While I currently have the black iphone 5, I miss, from time to time, the form factor of the 4(and 4s). It felt great in the hand and it was just beautiful.
The leap in performance and style the iphone 4 made is something we may not see until Apple decides to increase the width of the screen as well as make the back entirely metal. In other words, that iPhone prototype we saw a while ago.
Apple needs to come out with another iPhone 4 next gen type of phone. The i4 over the 3GS was a MASSIVE update, since then the 4S and even the i5 just seem like more of the same, nothing new.