The hybrid classes are generally just stronger. I honestly just perform the worst with warrior and ranger. Character stats are much more flexible in Dragon's Dogma than in Dark Souls, though-certainly so for the hybrids. Magic boosts the magical damage of elemental weapons and the buffs you cast on them, so magic is useful even for a physical class such as Assassin. (though I expect much less so for a warrior)
I think a dedicated Assassin has the highest damage-per-second out of any class, (gale harness+hundred kisses eats through basically anything) has fast bow work, has near -auto kill attacks for both the sword and dagger, (clauraudiance and masterfill kill) and the can RUN.
Mystic knight can definitely be an excellent tank-or a machine gun and landmine. They get the best shields, heavy armor, and can enchant the entire party's weapons. They're also the only class that can curse things.
Magic Archer makes using a bow very easy-they have homing arrows. I definitely found there damage to be lower than as an Assassin, though. The magical dagger skills are really cool. (though curse is much more effective on you than on enemies)
Always have a healer pawn with you-that means a mage with an Anodyne spell, and preferably with Healer as his/her main focus-or you can fulfill that role.
I also suggest that you never spend rift crystals on hiring pawns. Save them up and spend them on items from the rift crystal shop-one item will let you change you and your pawns appearance at any point from the main menu. There are also additional character hair, makeup, eye and skin colors you can buy from the shop-and items that change what priorities you pawn has, such as healing, who it attacks, or how frequently they buff you.