Dot 4 or Dot 5 Brake Fliud?

DOT 4 and DOT 5 fluids are completely different creatures.

Oversimplified, DOT 4 is the "HD" version of DOT 3, and basically it just has a higher boiling point than DOT 3. Both of these are glycol based, and are very hygroscopic.

DOT 5 is silicone based, and has a higher boiling point than either DOT 3 or DOT 4. It's also less hygroscopic than the glycol based fluids, which can be seen as an advantage.

Use whatever you feel is best, but whatever you decide, never mix the glycol based fluids with DOT 5.