I'll be doing an HID retrofit on my 92 Eagle Talon and its come down to the Audi S4 projectors and the Hella 90mm projectors. What I want to know is which ones overall will over better lighting, I just want the brightest and best down the road lighting.

Whats better?

I would not be as concerned about that choice as the overall install plan. The DOT Audi A4 version is somewhat tuned down compared to ECE version. Something you might want to consider is price. The Hella 90mm HID is practically not available used, ECE Audi A4 is sometimes available on ebay, and DOT Audi A4 version is always available.
Another choice is the ECE Golf IV OEM HID unit. It is the smallest of them all, which should make it easier install.
Sorry, I couldnt be more specific. Like evrybody else on the board here, I'd like to test all units, but its a costly adventure.

Just to add. The other thing is how you are going to mount them and whether unit weather proofness is a concern. Hella 90mm units are weather proof. Audi A4/S4 or any other OEM projector you will need to deal properly in your Eagle housing.

The other question is. When you refer to Hella 90mm units, do you mean that you are going to convert H7/H9 units or get actual Hella 90mm HID ones? Could make a difference to the price and the amount of work you would have to do.

I'm talking about the Hella H7-H9 halogen projectors, the HID's are too expensive. As for fit the S4 will fit, I have seen pics of them partially installed in the Talon housing and I can see that they fit. They will simply fit right into the reflectors and still use the stock adjustment. There will be only minor trimming to fit them so they will be weather proof as they will be sealed.

After doing some more measuring it looks like the Hella's will just be too big and require way too much customizing to fit. Now I know the S4 ECE spec projectors are better than the DOT, its just finding them that will prove to be challangeing. But still are the S4 DOT's worth it or am I better off looking for the ECE?

Is there a differnce between the A4 ece and S4 ece and, if so what are they, is one better than the other??

The A4 and S4 are the same as far as I know.