What's the best way to use mt knights?
Either wait a few turns 2 see how the fights going then send them in 2 try and out flank other company's.
Or send them in early as a heavy hitter 2 make a dent in the enemy's formations?

Depends much on the situation, I normally hold them back and threaten my oponent, MT knights are not Super ubber elites, but they are a grave threat when they charge specially leaded by a powerfull hero or character with decent fight value.

Keep them behind you troops as a safe bet, this way they are always able to harass flanks, regardless of who won priority.