My DM is running the "Bastion of unborn souls" or some such. We have fought several Balors sometimes multiple Balors at the same time. Let me just say I hate them so very very much. Twice it was almost a TPK when they exploded, only the fighter left standing. I will share with you the tactics we have learned for fighting Balors.
#1 Disarm, disarm and disarm.
#2 Wizards run or diminsion door on your first action 200' away and cast. If you can not get that far away you had better have a wall of force ready and cast it early.
#3 Clerics run like hell after casting a link spell on the warrior, you can try to implode or banish but I recomend hanging out with the Wizard.
#4 Do not fight Balors in or near your own home. Your home will be destroyed.
#5 Did I mention disarm?
#6 Rogues, run circles around the Balor in full defence untill you can get in a good shot.
Those are the classes in our game so I can not comment on other classes tactics
We did however manage to get one of the swords by disarming and picking it up
I really hate Balors.