I have been in the sewers below the temple district and have not found Keldorn. I have already been given the Unseeing Eye quest by the temple of Helm. Is there another trigger in the story?

Also, who should I take Jaheira or viconia?

Thanks in advance.

Keldorn is supposed to be in the West end of the sewers, fighting a zombie. If he is not there, check at the Order of the Radiant Heart. Deciding between the two depends upon your alignment. If you are good, take Jaheira, she is a good fighter/druid, and grab Anomen or Aerie if you want the clerical spells that Druids do not get. If you are evil though, go with Viconia. I do not know anything about her, as I never made her part of my party, but I have heard mixed reviews.

You can't really compare them, they do different things. Viconia's a cleric, and a damn good one. Jaheira's a tank/fighter with druid spells. Give her a strength booster and you'll be able to make a better judgement. She's a killing machine with the blackblood club, good with a sling, or, if you want to give her a couple of proficiencies with spears, the impaler.