Some Commanders are super strong. Others … suck. Some are even simple „Vanilla“ Creatures, meaning they don’t have any abilities at all, and are just a creature with power, toughness and a creature type like the depicted Barktooth Warbeard.
Okay, we do agree: Noone would seriously play such a commander. And while its body is not apropriate to modern day’s cards mana cost / body relation, the simple fact that Commander is normally about the fascination to have a card (your Commander) always available and so you can use its abilities to interact and synnergize with other cards is what makes Commander that interesting, cool and fun. As a fact, you can also visit EDHRec and see, that there are commanders with hundreds of Decks build around him/her, and others with few Decks. So this popularity also points out that some commanders might be stronger (and therefore more popular) as others.
But – back opn topic – while a vanilla legendary creature is clearly underperforming and unwanted as a commander, can you distinguish what makes a card a better or stronger commander ?
Combo.
Some Commanders do offer the possibility to go into infinite combos or do a lethal damage punch out of nowhere. While some combo cards like Ancestral Statue for Animar are banned, other cards still exist and can occur. Commanders which have easy to assemble combos (therefore known as combo-commanders) are of course of a higher threat level than these who can’t go infinite.
Yes.
No.
Er…
Okay, we are once again argueing with one of Magic’s most controversial topics: can you categorize certain Decks / Decktypes as „Tier-Levels“ or stronger or weaker commander per se ? We said in the past, that this is quite hard, as local occasional funplayer’s (who might also have a limited budget) „Dragon Theme Deck“ version of Niv Mizzet Reborn may not be as spicy as a tournament dude’s deck.
But of course we can try at least and soothsay a potential – and efficiancy of a commander card.
Here are the 7 goldenrules / attributes which give a Commander more potential than others:
Re-Castability.
This might be the most trickiest to rate: while CC 
Commander is of course cheaper than most others, it doesn’t necessarily mean he’s stronger. But the tendency is what counts, so cheaper commanders can normally played more often during a match, and are more present. While Gisela, Blade of Goldnight is a decent commander, its color identity is lacking green for efficiant ramp like the Maelstrom Wanderer offers, nor does she ramp by itself like Golos, Tireless Pilgrim. You can be lucky to have her out two or three times in a match. Other sommanders can be cast much more often: They don’t increase casting costs like The Locust God as it is cast from your hand again, or it offers active ramp or at least provides green as part of the color identity. (a green commander for CC 
is much easier to play as a blue one!) And of course a general small CC helps, too, especially if the critter has more power and toughness and stats like flying, lifelink and so on than it would be usual (e.g. Atraxa)
(Card) Advantage.
As old as magic itself, every player knows that card advantage is good. If your commander actively gives you an advantage of more lands or cards, he’s certainly good. The Maelstrom Wanderer is such an example, where a commander gets insanely and quite unavoidable card advantages, that were simply too good, so it got banned. Most Planeswalkers also provide acertain kind of card advantage, as their effects are quite unavoidable (see below) and the planeswalker remains in play (most of the time), so the effects will reappear every turn until the Planeswalker is handled – a Lord Windgrace can achieve a semi-Lock with a Wasteland and provide lots of card advantages. These effects are even more potent if they are for free and unavoidable: Azami, Lady of Scrolls is actually better than Arcanis the Omnipotent, as Azami always draws a card and replaces herself, but Arcanis has to survive a turn to get active.
Resistant.
Some Commanders are harder to kill than others. Best examples are commanders including the keywords „indestructible„, „shroud“ and „hexproof„. But why is this such a big deal ? As commander Decks are singleton decks, the amount of possible answers are limited: for example, red can’t kill a commander like Keranos, God of Storms very easily. Besides Chaos Warp you need to be tricky and use All is Dust or thelike, but these cards are, as said, quite limited. You have to draw them, and once played, you know your deck might mnot be able to recover these cards or have any more of these answers anymore included in the rest of your deck… but the commander comes back again – and again – and again. So Sigarda, Host of Herons is potentially stronger than Sigarda, Heron’S Grace, as it is much harder to handle, and Wrath of God like effects may be limited in your deck as a countertool.
Passive Gains.
If your commander grants you a benefit on its own, without manacosts, or hinders your opponent, that’s cool – and efficient. So this means your commander has a game changing impact as soon as it hits the table. While a Danitha Capashen, Paragorn does grant you a benefit, it is not on its own but just interacts with other cards – still cool, but a Grand Arbiter Augustin IV is certainly more powerful, as once on the table, its effect messes with your opponents, and it costs you: nothing at all. Next to passive gains without other cards are of course passive gains interacting with other cards without mana : Atraxa is such an example: it proliferates your AND your Teammates counters – without you paying any mana: passive gains throiugh and through.
Unavoidable.
Colorful.
Wait. A commander should be better / more efficiant if it has more colors ? Yes. Though more colors offer the risk of being color screwed (you don’t have the right mana to play a card, e.g. no mountains but have lots of red cards in your hand), the more colors you have, the more interactions with different cards are possible and the more color strengths can be used: so while a white deck has barely any counterspells, a blue deck has. A black deck has hard times to handle artifacts, but green has lots of answers. Just splashing a bit of whiote offers you cards like Swords to Plowshares for cheap removal. So, the more colors your commander has, the more efficiancy potential he has got. Keep in mind we are talking about potential: of course there are really nice and strong mono-colored decks out there, but some color combinations do really have a harder time out here, and player’s who play partner commanders often tend to do so just to have access to the „best-of“ cards of three to four color options possible.
So, that’s it ?
At least it is a try – we said multiple times, catagorizing Commanders and Decks in „Tiers“ or Powerlevel „strong“ and „weak“ is not as easy and always failure-free as it might seem. But you might get a clue: If your commander is a Planeswalker and green – it might be a better deck. If your commander is a God with indestructible… again, it might be better. If your commander is Nin, the PainArtist, which needs to be tapped, is non green, has no Protection on its own, doesn’t provide too many color-identity options, has no passive benefits – you guess it: he is potentially less efficient and powerful than other commanders.
Nevertheless … as always: just play and have FUN !
Your Teamcommander Team !