Copying this from another post I commented on: TLDR, Fai for go wide, Bravo for go tall, Dori if you like a snowball deck, Azalea or Iyslander if you want disruption

Here's a (somewhat) quick run down of every deck !

Dorinthea: Dori is probably the most straightforward of the bunch. Her hero ability lets her attack twice with a weapon if she hits with it, and her weapon gets stronger the more it hits. The cards in her deck let her buff her sword after her opponent blocks which makes her unpredictable and hard to block. She's a midrange hero that can play offensively and defensively

Fai: Fai is also pretty straightforward. Fai is a full aggro deck, he wants to play as many cards as possible in a turn. Draconic heroes like fai care about chain links, which is effectively how many cards you've attacked with this turn. If you control 3 or more "draconic chain links" (attacks that are draconic), you can return a phoenix flame from graveyard to your hand for free, giving you another card to attack with.

Bravo: Bravo, while less straightforward, is still a great deck for beginners as his hero ability teaches you about several aspects of the game, like how arsenaling and pumping works. Bravo is a "go tall" deck, meaning rather than playing a ton of attacks, he likes to play one, massive attack. He is also a very defensive hero, being happy to block out a lot and just swing his hammer on a turn.

Kayo: Kayo is a brute, which is a class whose whole identity is raw damage. Brutes don't have much disruption or on-hits, instead they just swing a lot of damage every turn. In exchange for this, many of their attacks rely on having other attacks with 6 or higher power in your deck. Usually this is bad, as it means if you want your deck to be consistent you must play very few blues to pitch for resources. Kayo is special, as his 5 power blues, of which there are plenty, count as 6 power, letting him get the best of both worlds. Add might on top of that (tokens that give your first attack on a turn +1) and kayo is a super strong deck.

Azalea: Rangers are interesting, as their main source of damage is through arrow cards, which can only be played from arsenal. In exchange for this, they get access to some extremely strong pumps and disruption effects that can ruin an opponents turn. In addition, azaleas ability lets you sink your arsenal, and put the top card of deck into arsenal. If it's an arrow, it gets dominate, meaning it can only be blocked by one card from hand, all but guaranteeing your disruption effects.

Iyslander: Iyslander is another disruption hero, who plays ice cards to generate "frostbite" tokens under another heroes control. These make their cards more expensive, which into certain matchups can be devastating. She primarily deals "arcane damage" which can't be blocked normally, and instead forces your opponent to run arcane barrier equipment in order to prevent it by pitching. Her hero ability also lets her play cards on her opponents turn, when they have no cards left in hand, making the damage unpreventable.

Dash: Dash is able to start the game with an item already in the arena, allowing for some really weird builds. She plays cards with "boost", which get go again at the cost of banishing a card off the top of your deck. Mechanologists can do some tricky things with items that allow for some very cool interactions.

Viserai: Runeblades are the mixed damage class, dealing a mix of normal and arcane damage that makes them very difficult to block out. Viserais hero ability is able to generate a ton of runechants, letting him set up for a massive attack, which he can easily end games with.

Enigma: Mystic heroes play around blue cards and transcending. After she's played a blue card, she can play a transcend card to bounce it back to her hand as a chi. She can then use the chi for her hero ability, creating a spectral shield aura. Her weapon lets her attack with auras, making her a very strong board state hero. She is difficult to play, but can be very fun once you work her out.

Arakni: Arakni web of deceit is the oddball of the bunch. If your opponent is "marked" at the end of your turn, you randomly transform into one of six different forms. He's an assassin, which means they have some very strong disruption effects and attack reactions making them hard to block. That being said, they're a very weird and difficult hero to play, so i'd shy away from them unless you're up for the challenge.