That's a tough question because some of the schools are more divided by role rather than playstyle. For example, if you want to be a pyromancer, I don't think you're going to be very effective with just Invocation. You're probably going to need fire AOE from conjuration, fire shield from Abjuration, etc. Only the physical schools seem to be clearly defined. (For example, if you want to be a ranger, you'll obviously go into Marksmanship).
Personally, I have a really hard time deciding. I like battlemages, I like healing, and I tend to gravitate towards marksmanship in action RPGs but often get bored because it's often a 1 button spamfest. For Fractured though, I am looking at a few possibilities right now:
1: Assassination + Marksmanship.
Ranged and stealthy, always a cool combination. Sneaking up to my targets and pinging them from afar, very deadly in PvP aswell. Both schools also appear to have a lot of synergy. Both schools use Dexterity and Perception as their stats, making it very easy to build around. They also both mention poisons, so I wonder if there's synergy there aswell.
2A: Martial Arts.
Imagine a Beastman storming at people and kicking/punching them to death. Depending on the feel and animation of the abilities, it could feel very feral. Combined with Assassination, it would probably be a pretty lethal combination, and an alternative to stabbing things in the back.
2B: Martial Arts, monk-style.
Monks. Many games have them. WoW monks, Diablo 3 monks, etc. Martial arts + magic and healing. This sounds like a very fun combination to me aswell, but might require investment in too many different stats to make it work. With Martial Arts focusing on Dexterity and Strength, and the magical schools focusing on Intelligence, that's 3 out of 6 stats that I would need to invest in to make it work. It's probably possible, but I might end up being mediocre in every stat then.
3: Battlemage.
One of my favorite playstyles is to combine magic and melee into one coherent playstyle. In Fractured's case, I would probably be looking at a combination of Warfare and Conjuration. With any luck, not that much investment into Intellect will be required to make the mage side of the build work. Getting a few Conjuration buffs will probably work out fine. I mean, the one revealed Conjuration ability appears to enchant your weapon with lightning and that looks like it's made for melee.
4: Engineer.
I love Engineer playstyles. The Engineer was my favorite class in Warhammer Online. Considering the fact that humans are living in a steampunk setting, it will probably be possible to build one. However, since humans are the only ones who can benefit from human technology, I would have to roll a human to be able to play one, and I don't know if I'm willing to do that. It would very much depend on the justice system on Syndesia. If steampunk abilities exist, they can probably be found among Marksmanship (guns) and Conjuration (deployables). As Marksmanship and Conjuration use 4 stats in total, it would probably be a tough build to make though.
5: Full support.
Depending on the group play, I might end up going with a very support heavy build. The build would focus on Restoration, probably Abjuration and perhaps Divination. As all these schools depend on Intelligence, it will be an easy build to make.
These are the builds I am currently thinking of, but without a full ability list, I can't make a final decision. 
