Albus Dumbledore vs Gandalf the White
Both are bloodlusted so dumbledore can use the unforgivable curses and gandalf can go all out.
This is considering gandalf can't come back after death and dumbledore has no horcruxes.
Battle takes place in an open field with rocks and a small lake around.
Opponents start out 35 feet apart.
Round 1. They have no prep or understanding of each other
Round 2. They have knowledge of each other.
Let the battle begin.