I've finished with WK, and am about to take on Demogorgon.

I just wanted to know what method is best to get the MOST xp.

Should I read the scroll, then not forgive the priests? Should I fight and beat Demogorgon, then forgive the priests??

Help me out. Spell out the most xp rich way of dealing with Demogorgon.

Kill them, kill them all. (I believe that's a quote from "Hook").

Make sure you get the scroll -- it's worth 25,000 xp
(xp, normal experience points divided between everyone -- qp, quest experience points given to each character)
Sealing everyone in and running away is 80,000 qp
Killing Demogorgon is 100,000 qp
Talking with Orden after the slaughter is 20,000 qp (I don't know if you have to forgive him -- I did)
You can make a real killing here in xp's if you allow Demogorgon to gate in a lot of allies -- everytime you kill off his gated demons, he brings more to the party. The good part is the xp's (Balor 26,000 xp; Cambion 18,000 xp; Glabrezu 12,000 xp; Marilith 23,000 xp). The bad part is you have to survive all these demons.

Good Luck.

I tried that aproach. Standing off and killing Demons was not too much of a problem, but when I went after Demogorgan himself he called in 12 Glabrezu. That was a very hard fight which continued after the demise of the big D.
Yet again I had to raise Minsc - he seems to make death a habit. The experience was good, but there was a slight whiff of cheese in the air.

Path to most XP as far as I know:
- When you get to Demo, read the scroll, and get sealed with him
- Escape with his help, and make the knights go in themselves
- Take the scroll from the ghost, and use it
- Go in and kill Demo

Theoretically using the 2nd scroll should prevent you from going in, but it never does in my games (with latest TOB patch)