[Nerull]

Aerie is good if you use her right, especially with the right equipment. Having her cleric spells sped up by the Robe of Vecna can be very useful.

In many of my games, Anomen ends up in the party. He's strong enough of a fighter to allow him to tank (especially if you give him the Gauntlets of Dexterity and ***** in a melee weapon). If he passes his test, he is a solid cleric, too. He may be annoying, but very useful in the party.

Jan is also useful, if annoying. Multiclassing rocks in ToB, and he is a strong thief and solid backup wizard. Definitely a winner in my book, if he would just shut up.

My vote for the worst: Cernd. If this were 3rd edition and he had access to feats from the Masters of the Wild book, give him Natural Spell and he would rock (cast spells while changed in form). Can you imagine him in werewolf form casting Nature's Beauty? Ironskins? But he doesn't have that feat, so he can either change form or cast spells (at least Jaheira's shapechanging sucks enough that you rarely use it, so you end up keeping her in regular form and just casting spells with her).