If you plan to actually tank as a warrior and go offense for holding aggro/extra damage, then I would suggest keeping a shield (preferably orange) and good 1H weapon(s) in addition to a greatsword. Sometimes you just have to use a shield for survivability.
Anchaii gave some excellent advice on Warrior KP. If you like to PvP I'd highly consider the +2s Intimidate duration too.
For Knight, absolutely put 5 points into the P-Atk talent. I'd argue it's the single best talent in the game: 5 points, no pre-reqs for 10% P-Atk. Most Knights tend to go towards Evade, and offensives ones are probably getting crit rate as well.
I can't say much about offensive Templars other than you'll probably have to look for blue armor with Magic offensive stats, which is cheaper yet much more difficult and time consuming to find.
As far as Certs go, it depends. When you're using a 2H Weapon 4-Green certs is an excellent combination, especially since Green have some of the best certs around.
With 1H Weapon I'd still highly recommend Hunter Crit damage and Engi Crit rate or Hunter luck. You have some more options now. 4-Orange certs is nice, but can be difficult to do without sacrificing too much.
The Yellow Evade/Malice/Defense certs are always decent, and Warrior can use Taunt + Rapier Attack for 12% more Bloody Attack damage. Knight on the other hand uses Rapier Attack + Muscle Flexibility for 8% Judgment storm damage. You don't have to use either of these combos as they aren't spectacular, but better than 2% Str.
Personally I find it difficult to work 4-yellow certs into my Tank builds as they just don't offer enough offense for my taste. They are absolutely worth using if you're having trouble staying alive (though only if you're using a shield).