Olbermann was the worst of the MSNBC lineup (with Maddow being the best, Chris Hayes being a pretty good substitute for Maddow, and with O'Donnell and Ed Shultz being almost as terrible as Olbermann). He makes liberal pundits look bad. I'm just happy that Maddow is uber-professional and makes liberal pundits look good.
Maddow and Matthews were the best of the MSNC lineup, IMO. I think Cenk Uygur did a good job on MSNBC too.
Matthews has a lot of knowledge, but he needs to shut up once in a while. I actually like O'Donnell, and Schultz is hit-or-miss. Sharpton is still not very good, but his show is much better than I expected. She's not on weeknights, but I LOVE MHP. To rank the weeknight hosts:
Maddow
O'Donnell
Schultz
Sharpton
Matthews