I have been playing RFO for some time now. I already tried the Cora and the Bellato races. I'm not really an expert in this game but here's what I think of the three races in the game. ^^
Cora: Great offensive firepower in terms of their spiritualist classes especially the warlock class. Summoners add versatility due to the different types of anima they can use in battle. Their warrior classes are tough but not as tough as the accretians but have good attack skills. Their rangers can provide great support (especially the archer class who has the hold class skill). Their specialist class is not quite as good as the other races. I think that the cora has the lowest def of the three races in the game which offsets their high damage potential (just my opinion).
Bellato: Their specialists(driver class) have the ability to pilot MAUs(Massive Armor Units). These MAUs are great in spearheading assaults (due to their large amount of hp) but can die really quick if left alone without support for too long. Their warrior classes can deal a lot of damage and have a good def rating. Their ranger class can provide good supporting fire because they can almost spam their attack skills(the desperado class has a skill that can lower the delay time of their attack skills). Their spiritualist classes (although the damage dealt by them are not as high as the ones that the cora force users can deal out) can provide support thru the use of healing force skills.
I also tried using an Accretian but only in a short amount time. They are tough(I think they have the highest defence of the three races). Their race specialty would be the use of the launcher weapon which is very dangerous in large groups(especially with their ranger class that specializes on the use of launchers). They also have a ranger class(dementers) that can self destruct causing massive damage to anything within a certain distance around them. Their warriors are very tough and difficult to kill (especially when equipped with int armor and upgraded with talics). Their specialist classes can also use grenade launchers which can use different kinds of ammunitions (I think they have an ammo that can debuff and another one that can stun).
Focus, Control, Conviction, Resolve.