Knights are good for big, messy fights.
5 knights or more attacking together will push any opponent back a bit, or halt any advance.
1vs1, though, you are better of picking a MMA or Vanguard.
Knights are the core infantrymen, their greatest strenght lies in fighting with the group, and being the iron fist of the team.
You will lose 1vs1 vs an experienced MAA if you are both as skilled.
But a MAA will never be as useful as a knight when it comes to holding the line.
Throw 8knights vs 8 MAAs in a narrow map, and the knights will suddenly have the advantage
Remember the melee class roles:
1. Knight - The heavy and slow one, thus the linefighter, the most group reliant.
2. Vanguard - Heavy damage and fast, thus the heavy flanker, a little less group reliant.
3. Man At Arms, thus the skirmisher, ideal loner.
If you are trying to skirmish as a knight or throwing yourself into a big melee as a MAA, you are doing something wrong :P
It can be done but is definatly not favourable.