Simple on this.

Where is Keldorn,how do you get him and is he better than Valygar?

This question thing is addictive!!!

Heh, I know what you mean, lol.
Keldorn can only be found once you accept the Unseeing Eye quest which starts in the Temple District. He can be found in the NW corner of the entry level of the sewers.
If you have not accepted the quest, he will not appear.
I can't compare him to Valygar as I have not had him (Valy) in my party. Keldorn, however, was in my party throughout most of the game and he has some useful abilities:
1. He can cast dispel magic (at twice his level, I believe); useful for fights against mages.
2. He can cast true sight; save your mages from having to memorise that spell. Useful against invisible creatures, or mages that have cast a spell like mislead, etc.
3. He can wield Carsomyr (aka the Holy Avenger).

The only bad thing about him is his dexterity - it's bad. However, there is a gauntlet that raises DEX to 18, so I gave him that.