The dog companion is widely regarded as the best first-companion choice regardless of your class simply because it does the most damage. The cleric (healer) companion heals so seldomly and for so little that it really isn't worth it unless you are playing a Guardian Fighter who is already fairly competent with the block so that the small heals she ends up casting are just topping you off since you are always fairly high.
The dog does a decent burst damage attack and has a knock down that he uses somewhat intelligently.
Of course, this is all based on the first 20 levels or so. Once you max out the cleric companion for instance, she is healing pretty well as she has her HOT as well as her standard heal. Naturally all of the starter options are going to be worthless once they hit companion level 15 (this will probably take a good 20-30 levels for you because its easy to forget to send them to train). That is until they add the companion training books that allow you to raise their caps.
This may end up somewhat long, but here goes!
First of all, what exactly are Action Points?
(I just took the time to add this to the official wiki :D @ wiki )
Action Points are the method by which a character's Daily Powers are recharged. Each character has a gauge represented by a D20 in the middle of their Combat Action Bar. This gauge refills as the character gains more Action Points. When this bar is filled by the attainment of Action Points, a character's Daily Power is available for use. The use of a character's daily power depletes this gauge and a character must once again perform actions which grant Action Points to refill it. Each Class has a different set of things that cause the character to gain Action Points.
What abilities gain Action Points?
Great Weapons Fighter :
Encounters:
Battle Fury - Increases your Atwill and Encounter damage as well as
Action Point gain for brief period. In addition, when first activated
your Stamina is refilled. This power may be activated while moving.
Indomitable Battle Strike - Savagely strike your
target to shows your other foes the fate that awaits them. After
killing a target with this strike, you gain bonus Action Point, and
nearby enemies are briefly Marked. Marked targets take additonal
physical damage until they attack you.
Feats:
Unstoppable Action - You gain 5/10/15/20/25% bonus Action
Points for dealing damage while you are Unstoppable.
Guardian Fighter :
Encounters:
Into The Fray - A fierce battle cry that temporarily increases your
adventuring party;s deflect chance, Run Speed, and Action Point
generation.
Ability Score Bonus:
Constitution - +1% Action Point Gain
Feats:
Action Surge - Gain 2/4/6/8/10% more Action Point for damage reduced
by your damage reduction.
Improved Vigor - When less than 50% health, gain 2/4/6/8/10% more
Action Points.
Martial Mastery - Taking damage while not using Guard now builds
Action Points. You gain a bonus to this value based on your Damage
Resistance.
Trickster Rogue
Encounters:
Bait and Switch - Jump backwards, dropping a decoy in your place. Any
enemies that are near the decoy will attack it instead of you. Gain
Action Points when the decoy is hit by an enemy.
Feats:
Action Advantage - 2/4/6/8/10% bonus Action Points for dealing Combat
Advantage Damage.
Cunning Stalker - While Stealthed, you build 4/8/12/1/20% more Action
Point.
Action Rush - Your encounter Powers have a 15% chance to grant
3/6/9/12/15% of your Action Point.
Thrill of the Kill - When you land a killing blow, gain .2/.4/./.8/1%
of your Action Point.
Control Wizard
Ability Score Bonus
Wisdom - +1% Action Point Gain
Feats:
Controlling Action - Gain an additional .2/.4/.6/.8/1% of your max
Action Point when you cast a control power.
Critical Power - When you land a critical hit you gain 1/2/3/4/5% of
your total Action Point. (10 second cooldown)
Devoted Cleric
Encounters:
Prophecy of Doom - Target has lowered Defense for a medium duration,
and if target is still alive after this time, They take a large amount
of damage. If target is killed during this time, you gain a large
amount of Action Points, and this power instantly recharges.
Feats:
Healing Action - Gain 1/2/3% more Action Point whenever you use a
Healing ability.
Ability Score Bonus:
Charisma - +1% Action Points Gain
Class Feature:
Holy Fervor - Your attacks generate 5% more Action Points. Rank 2:
+5%. Rank 3: +5%
Also, if you mouse over your AP meter while it's not full, it will tell you what fills it. Another cool thing to note, is that the Recovery mod raises AP gain by a percentage.
For example, 2,982 Recovery is +49.3% AP gain.
Best Answer
Mitigation in Neverwinter means exactly what the actual definition of the word means.
So for example, Ray of Enfeeblement has the following description:
SO, what this all means is for a period of time you've lowered the targets ability to reduce the damage from your incoming attacks.
Well how is the target mitigating (there's that word again) damage from your attacks in the first place? Good question, glad you asked.
Damage Resistance IS mitigation.
Damage Resistance decreases the amount of damage you take from incoming attacks. Defense helps to increase this stat.
Therefore, if you put this all together using what you just learned (stay with me now) it goes something like this...
"Target X" has a damage resistance stat 21.2%.
You cast Ray of Enfeeblement on Target X which reduces his damage mitigation by 15%.
Over the next several seconds, Target X's Damage Resistance (ie: mitigation) is effectively 6.2%
21.2% - 15% = 6.2%