Ok first off not many of the forsaken have actually "died". The fact that they can be reborn, and are basically immortal is part of their power. Only balefire, "trapping" their soul or converting to the light can defeat them.

the only forsaken to actually be killed off are Be'lal, Rahvin, Asmodean, Sammeal, semi and Grendal. 4 of which were done in by balefire, one converted and had his chord taken away, and one was absorbed into Mashadar, a mass of evil souls.

Be'lal I think had a fairly good plan. At that time he knew Rand was a country bumkin that should have fallen with little ease. Had he won he would have gained Callandor and the girls to link with after they got turned to the shadow. Unfortunately the soon to be legend Moiraine pops out and BF's him.

Rahvin, well what can I say he got attacked by Rand, he was trying to lead him toward Sammael which would have worked had he not messed with Rands future mother in-law. bad luck I say.

Asmodean I still believe he did the best job, he was so close to ultimate power, like Demandred close. Again Rand got on his tail and hunted him. This is what lost him his immortality. Later he got off in a way that no one could have prevented. He was the weakest and yet his run was the best.

Sammeal was stupid. He did lure Rand away from his back-up, however why not lure him to the blight? or somewhere he had control. he off all the forsaken had this planned and still failed.

Semi failed because she was semi. Arrogance got her captured and her sadistic nature got her killed.

Grendal, if she's dead , her death earns her a seat on the short bus...If the Dragon Reborn cometh and you know full well from 3 books previous he has Callandor and the CK access key you don't sit your ass around and wait for a confrontation...plain stupid.

At the end of the day 6 forsaken are "toast", and only 1/2 died through incompetence.