All stats you need for any class. (just to make one thing perfectly clear for all who don´t know yet) are found in your own personal codex flaged under "persons of note" so if your indoubt of what stat your specific compagnioon uses click "L" flag codex and so on. and to make one more thing clear most of your compagnions use the same stats as your self and perhaps one other period.

cheers good hunting

Hutta
- Gauntlet - Level 3
- Tools of the Trade - Level 2
- The Last Flight - Level 4
- Big Chief - Level 6
- Settling Accounts - Level 7
- House Cleaning - Level 8
- My Sponsorship - Level 9 [Mako]
- Escaping Hutta - Level 11

Dromund Kaas
- The Hunt on Dromund Kaas - Level 9
- The Huntmaster - Level 9
- A Musty Trail - Level 9
- Family Cleansing - Level 14
- The Spy Game - Level 15
- The Melee - Level 16
- Joy Ride - Level 17 [Spaceship & Start Chapter 1]

Balmorra
- The Balmorran Target - Level 15
- Pirrell's Ambitions - Level 15
- Chaos at the Droid Factory - Level 17
- Down with the Queen - Level 18
- Bait and Switch - Level 19
- Meeting the Admiral - Level 19

Nar Shaddaa
- The Enemy of My Enemy - Level 20
- Economic Boom - Level 21
- The Underdogs - Level 21
- Catching Zees - Level 22
- Industrial Espionage - Level 22
- Professional Courtesy - Level 23
- A Dangerous Auction - Level 24

Tatoonie
- The Tatooine Target - Level 24
- Tracking the Smuggler - Level 24
- Confronting Veeboo - Level 25
- A Barter With The Lady of Pain - Level 26
- Catching A Slippery Eel - Level 28 [Gault]

Alderaan
- The Alderaan Target - Level 28
- Spiking the Punch - Level 28
- Like A Rancor In A Pottery Shop - Level 29
- Silver Tongues - Level 30
- Kingmaker for a Day - Level 31
- Honor Regained - Level 32
- The Mandalorian Killer - Level 32
- Hail the Conquering Hero - Level 32
- Fortune and Glory - Level 32 [End Chapter 1]
- The Heart of Darkness - Level 32

Taris
- A Friendly Wager - Level 32
- A Family Matter - Level 32
- Imperial Bounty - Level 33
- To Walk in Dark Places - Level 33
- Geroya be Haran - Level 34
- Honor or Glory - Level 35 [Torian Cadera]

Quesh
- Endorsement - Level 36

Hoth
- A Dish Served Cold - Level 38
- Cool Reception - Level 38
- Digging His Own Grave - Level 38
- Fire and Ice - Level 39
- In Cold Blood - Level 40 [Blizz]
- Notorious - Level 41
- A Failure to Communicate - Level 41
- Laying Low - Level 41 [End Chapter 2]

Belsavis
- The Ferryman - Level 40
- A Flicker of Hope - Level 41
- Juxtaposition - Level 42
- Mnemonia - Level 43
- Where Few Follow - Level 43
- A Thousand Pardons - Level 43
- No Strings Attached - Level 44 [Skadge]

Voss
- At Arms Length - Level 44
- Nihilistic Mystics - Level 45
- Captive Audience - Level 46
- To Still a Bleeding Heart - Level 47
- Thus, Always, to Tyrants - Level 47

Correlia
- Hostile Takeover - Level 47
- A Queen's Ransom - Level 48
- The Thin Blue Line - Level 49
- Reckoning - Level 50
- Number One with a Bullet - Level 50
- Some People Just Need Killing - Level 50

I think it's because they are of the trooper/BH archetype, who uses aim. Same goes for Tanno Vik, Yuun and other non-Jedi looking melees.
You'd have to be a Jedi Knight or Sith Warrior to use items with strength. For companions, it means Lord Scourge, Ashara Zavros and Khem Val.

Otherwise, it would be a pain to find gear for them. All trooper/BH armors has aim as their main stat, and surely Jedi/Sith armor would look very out of character for them.

It's a little awkward. After all, unlike vanguard/powertech who stays in melee range but uses flamethrower/electric shocks, they DO use a real melee weapon.

Tanking:
As tanks go, Bliz turned out to be a major squish for me. I the gear I bought/made for him on Torian and found a much better tank.
I just got Scadge... BTW, this is the first companion I can summon as a guest. Cool.
I have not tried to gear Scadge yet but in looking at his talent list, he is a different kind of tank than Torian. Scadge has more AOE and threat gen ability than Torian.
So what you get with Scadge is a tank that can attract and keep more attention from multiple mobs while you AOE, where as Torian gets the initial attention but then loses it if you AOE.
Torian also provides higher single target dps which means that single targets fall faster.

In my play style, I like Torian. I'm a Prototype Powertech. I need to be in close like a tank to take advantage of my dps and interrupt skills.
So I send Torian first and then usually pull the multiple mobs off him as we fight.
Neither of us dies and the repair bill is lower.

I'll give Scadge a few quests so I can see if I like it...

I'm finding that he is a little more durable but lower dps which makes since given that half of his gear is avoidance and absorption.

Off topic but in direct reply to the guy above this comment.

Aim is the stat for droids and skadge because AIM is used to increase the damage done by tech abilities which would include most droid abilities and half of Skadge's.

If you look at all the stats on all player and companion characters and do the math, Power is the primary damage stat.
Bounty Hunter's main stat is thought to be Aim. Mathematically Power is worth .23 damage per point where Aim is worth .20. (Hover over your Ranged and Melee Bonus Damage to see it.) This is true in both Ranged and Tech.
Ex. Aim (869): +173.8 so 869 points of aim gives 173.8 bonus. 173.8 / 869 = .2
Aim does provide an increased crit chance but the math works out so low that I almost always take sustained damage over a 1/100 chance at a crit hit.

Strength and Aim are equal value for Scadge.
His Melee Bonus Damage values work out like this:
Strength = .20
Aim = .20
Power = .23
Tech Bonus damage does not employ strength, only Aim and Power. Based on the listed talents, EMP blast seems to be his only Tech attack.
Crit multipliers employ Strength and Aim 1:1.

It may be that BioWare gave Scadge the ability to use Aim based gear because it typically has Tech Power whereas Strength based gear has Force Power. That way they don't have to add another set of gear just for Scadge. ;)
Hard enough to find weapons for Scadge or Torian.
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As of 1.2 there are more Techstaff and Techblades in the game. This includes mod-able versions. :)

The reason companions use a certain stat is for one reason only, for most of them
Appearance of gear.

Obviously for the ones that gear does not show on the companion at all, the stat is chosen to go well with the class that gets that companion. Such as STR for companions of a STR class, AIM for AIM classes, etc.

The absolute perfect example to illustrate this is the Trooper.

The Trooper's companions ALL use Aim. This is because Aim gear all looks like trooper equipment(the visual style) and all of their companions are supposed to be "troopers" in Havoc Squad. Their CLASS is not trooper, but they are basically republic troopers(aka army troops). M1-4X uses AIM because the parent class uses AIM, but adding gear to him does not change his look.

There is one exception to the rule, which is the Ship droid companion, which always uses Aim for some reason.

Melee tank companion Uses strength as main stat

Vibrosword is weapon

Loves Weapons as gifts

Picked up near the end of your class story on Belsavis