As sentinel watchman I used Kira most of the game, though toward the end it became more challenging/more healing downtime so I started to use Doc more, though always Kira for main storyline missions and most dialogue option, and even the boss fights Kira was fine to use.
Rusk I never used, T7 was forced to use him for the doomsday quest which was really annoying, Lord Scourge i hate, the worst character Bioware have ever created to go with the worst voice acting in the game.