3. William T. Riker, The Next Generation
Some fans may argue that William Riker stayed on as Captain Picard’s first officer for too long. He was clearly ready to be a captain early, but stuck on the USS Enterprise for a long time rather than accept the promotion. However, this worked out for Riker, as he learned a lot from Picard, tempering his adventurous style to consider the greater good of the ship and crew.
The times Riker was in command proved his capability, tough but willing to listen to others as well. He and Picard had a terrific dynamic, sometimes conflicting, yet Picard wanted a first officer willing to point-blank tell him if he was wrong, which Riker willingly did. While Riker did eventually become a captain, he oddly seemed better in the first officer role, not as a follower but a leader in his own right.