Below you will find player suggestion on which party format to utilize and which heroes to prioritize levelling up/gearing up. This is more for newer players, or free to play slow (who need direction on which to focus) rather than for core veterans
Suggestion for core party is:
Cleric is a given, he is our only true way of healing, and that regen is sweet sweet. Death Ward of course is a welcome addition. I use his move - 2x atatck legs, for extra utility.
Fighter makes the party near immortal with massive AC boostingness. Barbarian can do a good amount of damage, but in harder content, I find it only clearable with a good Tommus (Counterattack + AOE AC+).
Bard is excellent for crowd control, backup heals, and that sexy sexy dominate. Squishy yes, but ranged attack, preferably with Boris for solid damage is a great utility hero.
Wizard is well, Wizard. massive ranged damage, potential to recycle Disintegrate every 2nd turn. need I say more. I chose Wiz over ranger, because the damage output is just that much higher. Ranger does have more utility, and if you have the right gear combo (legend bow etc) he may be a better choice, and is less squishier.
Paladin is a unique backup choice, for instances that may require alot of Restore options. This is also generally a pvp breaker, because crowd control is king in pvp, and Paladin is the anti-crowd controller.
Rogue and Warlock generally take second notch for me. I have them geared, but feel they under perform in comparison. Regardless, all heroes need to be levelled for pvp, but in instances of pve content, id go with the above, or personal preference (Tiefling with multi color just looks awesome)