Having played all 3 classes in this beta and gotten all the Iron banner class armors, I find every class to be pretty well balanced, its all about which grenades, weapon upgrades and armor perks you take into battle. My efficiency is pretty rock solid in all 3 classes. My hunter is my favorite to play with but I think my warlock is most efficient. The key is the weapon/armor perks. Combing the right amount of strength, discipline and intellect will dramatically increase your efficiency. There are 2 weapon upgrades i love above all else Glass Half Full:Increased damage to the bottom half of your clip, Obvious why i like this The other decreases the cooldown of your grenade for every kill it gets, don't know the name. Now combine this with armor perks that can also effect the cooldowns of your melee and grenade and things get incredibly powerful especially with warlock who's energy drain melee power reduces grenade cooldown. See where im going with this and why my warlock is so efficient. Remember warlock is a mage type character its more reliant on its powers, so combining a armor perk that reduces melee power cooldown with grenade damage with perks that reduce grenade cooldown from melee damage and the combined effect of energy drain and its a freaking beast. ALSO ORBS OF LIGHT!! Pay attention to the killfeed when you see xxx drops 1-3 orbs of light, find where they are and go get them they fill your super meter faster. For me I'd say Titan is my weakest class but thats because i haven't properly built it yet and i would probably end up going with its other subclass and make it more of a meatshield.
I have only played a Titan, but I have seen gameplay of friends playing other classes and fought them enough in pvp to understand their abilities to some extent. Personally I believe that all classes are fairly balanced. As a Titan I have incredible amounts of armor and can, most of the time, take out 2-3 warlocks/hunters before I am taken out by a 4th player. My build focuses on grenade CD and secondly the melee CD. I use an auto rifle that had great accuracy with low recoil, medium damage, but kills reduce grenade CD. With this rifle I can headshot kill 2-3 players before I have to reload, and the grenade CD helps as an opener/ranged finisher in fights. The armor helps substitute my lack of mobility, and it's my understanding that, while a warlocks super is ranged, it has a smaller aoe. A Titan must leap into the battle to super and get caught in the fire, but has a slightly larger aoe. Hunter's golden gun is different altogether and allows for more precision kills. I rely pretty heavily on my auto rifle for 90%of kills and use LMG when I get the chance. I've had a positive KD on all matches with my Titan and have been either 1st or 2nd each match on my team.