Summoner Was was first released in 2009. When I discovered it in early 2011, there were only 8 factions/summoners. Nowadays, not only are there 16 factions, but the original 8 factions now have second summoners as well!
These second summoners are discrete, complete, ready-to-go decks that simply share a faction name with one of the original 8 summoners so that their unit cards can be switched between decks. Despite the name, you don't need to buy them second!
So, if your entry point to Summoner Wars was the Master Set, and you're looking back on the original 8 factions wondering which of the two summoners you should purchase for each, I have the answer: Buy both! But, if you're just starting out and want to know which one to get first, use this guide.
Both Phoenix Elf summoners deal damage without the luck of the dice. As a result, they both tend to dictate the terms of battle. Both have low life and must be wary of possible assassinations, staying out of the battle as much as possible but striking hard themselves when needed.
The Queen is the more aggressive of the two Phoenix Elf summoners. In the right match-up, the Queen goes on the offensive herself, since she brings common units to her as blockers at the end of her turn and can also block with conjuration units. The Queen likes to have one or two big no-dice turns per game as her precise units ramp up their attacks temporarily and mow down units with absolute certainty.
The Queen's son, Elien is one of the most hateable summoners in Itharia. This is because he excels at defense-oriented efficiency, forcing you to come after him and punishing you for it when you do. Elien can pull nasty tricks by dealing direct damage anywhere on the battlefield and destroying Champions in one turn that you expected to battle longer.
The Tundra Orcs are giant reckless brutes. Their attack values are high but often rely on luck. They place extra walls--ice walls--on the battlefield, crafting ice fortresses for strong defense or extra summoning points.
Grognack himself is one of the most intimidating units in the game, rolling 4 dice in attacks and sporting 7 life points. His units are universally big and tough and all have potential for high damage output, if you're lucky. Grognack's deck is straightforward and a ton of fun for complete beginners. Freeze an opposing champion, save your magic up for the one and only Krung, and crush in your opponent's head with a rock.
Torgan fully embraces the Ice Wall theme. The guy can spit out Minor Ice Walls at will, cascade them across the board and summon units directly in his opponent's back yard. Torgan's units even get better when they're nearby his plethora of Ice Walls. Torgan protects and inspires his high-risk/high-reward common units, and is ideal for a player who wants the flexibility to play offense or defense.
The Guild Dwarves specialize in structures, both building them and destroying them. Both summoners have a special connection to the game's walls, using their own walls to their advantage and destroying their enemies', while even their weapons of choice, hammers, elicit imagery of forging their way to victory with powerful, skilled attacks.
Bolvi prefers building a castle to building an army. His deck is full of powerful towers which don't move but which are extremely difficult to take down. His fortress grows throughout the game as he enhances his towers with upgrades and supports them with architects, forcing his opponent to think creatively about their plan of attack.
Oldin teaches wall destruction 101, using both specialized events and units to this end. Featuring Gror, one of the most feared and powerful champions in the game who shakes the earth with his Hammer Quake attack, every card in Oldin's deck is straightforward and simple, making it one of the best decks to learn the game with.
The Cave Goblins are numerous, cheap, and expendable. The Cave Goblins gain strength in numbers and have an unparalleled ability to bring tons of units to the table and make the best use of all of them--especially the units who were summoned for free.
Swarm is a good word for Sneeks. Over half of his units are free to summon, and he empowers those units with extra attacks, gang-up tactics, and extra mobility. Sneeks likes to get in the fight whenever possible, and has sly tricks for keeping himself and his units safe at key moments.
Like Sneeks, Frick has a ton a free units and empowers them with extra attacks and mobility, but Frick is more of a precision assassinator than a swarm-oriented summoner. Frick and his units end up with a lot of range with which to attack from farther away multiple times, making it difficult to escape that last wound once he's got you wounded.
The Fallen Kingdom represents pure monstrous evil, with vampires, demons, and the undead making up their armies. The theme of sacrificing life in order to earn an advantage elsewhere and bringing units back from the dead drive home the undead theme of these demented summoners.
Itharia's legendary evil overlord, Ret-Talus has no problem sacrificing life for the win. He brings out champions cheaply by wounding himself and destroys his always-growing army of Zombies and other units in order to support those champs. Ret-Talus does not have to rely on the draw pile or even walls--he can summon a common unit from his discard pile next to himself every turn.
A prisoner-turned-disciple of Ret-Talus, Sirian breaks the summoner mold by healing himself every time he wounds an enemy unit. As a result, Sirian is happy to wound himself with over half his cards, gaining ridiculous advantages in exchange for his own life. Whether it is drawing extra cards, summoning units for free, or bringing units back from the dead, Sirian hits hard and fast while pushing the limits of his own vitality.
The Vanguards represent life and light. Angelic units and righteously-minded humans go into battle protecting and supporting each other while bringing judgement to their enemies.
General Farthen specializes in protecting his common units, via his own aura and by with events that stop the opponents in their tracks. Samuel is a beast to bring down with 8 life and the ability to even protect and strengthen himself. He employs high-life units who resist wounds and then punish you for not finishing them off.
Sera Eldwyn emphasizes healing and removes wounds from her high-life units even after they have taken damage. With an inherent ability to heal and priests who assist (as well as deliver judgment with extra powerful attacks), Sera is difficult to beat in the long game, as fighting against a champion supported by Sera's healing can be like taking two steps forward and three steps back.
The Jungle Elf summoners are momentum-oriented. They strike with speed, out-maneuver your defenses, keep you on your heels and strike with wicked combos between their powerful Event cards and animal-friend units.
Abua's ability to boost the attack value of any unit on the battlefield, plus the ability to get at a summoner who otherwise looks safe via Lioneers, Chant of Haste, Chant of Deception, and Miti Mumway, mean he's a great assassinator. But more importantly, Abua relies on his hard hitting units and combos of event cards to encourage creative play that overruns the opposing army.
Nikuya Na specializes in two areas. First, he introduces poison wounds that can slow down and subdue the hardiest of champions. Second, his array of events allows him to boost up his nearby allies for a turn at a time with extra-powerful abilities. As a result, Nikuya likes to be in the middle of the fray, poisoning nearby champs and boosting himself or his companions most turns.
Both Cloaks summoners focus on trickery, strategy, and deceit. The Cloaks win games by beating you at a game you weren't even playing, like stealing cards from your hand, attacking from places that seemed impossible to attack from, and generally being the most unorthodox faction in Summoner Wars, relying the most on brains and the least on brawn.
Jexik is one of the most common-friendly summoners in the game. Each round he gets an extra move on one of his commons, although it takes foresight to plan that move. Jexik's units fly around the board, stealing cards from your hand or vanishing all over the place. Opponents must beware the big turn: Jexik gets a one-time +2 boost to all his units' attack values via an event card, and he's always capable of an assassination.
While Jexik usually sits in the back directing his army from afar, Vlox is engaged in the thick of things, since he can copy the ability of one of his units each turn and can protect himself from attacks. Vlox players are creative, developing innovative strategies to steal, deceive and assassinate their way to victory.
Hopefully, this guide has been helpful in giving you a sense of both how summoners from the same faction work in tandem and yet how they diverge! Personally I recommend buying everything, but if you're just starting out, use this guide to help you decide what to get first.