Originally Posted by pyrobionic
What is the real differences? Which one is better in hot/cold or does it matter? And which brand would you recommend?
you should NEVER use DOT 5, since it is silicone based.
Get DOT 4 or DOT 5.1, and as long as it meets Audi specs you should be fine. Do a search of the archive and you'll get plenty of opinions: Valvoline, Pentosin, Castrol...
The actual make of the fluid doesn't make a huge difference, but whatever you do, don't buy DOT 5.
FWIW 5.1 is primarily for racing...I REALLY doubt you'll need that. Stick with DOT 4 and you'll be fine.
But you should SERIOUSLY start learn to use the Search function...since your questions are things that have been covered EXTENSIVELY.