Fabregas was good, eloquent and seems he's got a career in punditry when he packs the game in. Scott has been superb, as has Lampard. Bilic and Keane aren't my personal favourites but can see why people favour them.
For in-match co-commentary I'd say McCoist, who has been witty, interesting and should hopefully be invited back to do more.
Poor commentators who need to be moved on: Jonathan Pierce (he just sounds jaded, not sure there is any genuine enthusiasm), Mark Lawrenson (awful in pretty much every way), Danny Murphy (again, poor) and Alan Shearer (legend as a player, but he doesn't add enough insight about the game and seems to prefer to whinge).