I am not sure about Balance, but I hear it is very solid (A good balance druid dueling a good feral druid can be a good duel, taking 10-20 minutes, maybe even 30 minutes, from my experiences.
Robert is true, ferals are OP, but they aren't as OP, or as hated, as Robert makes them out to be. It's your choice, and both choices are very viable. I personally find Ferals more fun, because we are very viable in melee, while keeping ranged spells to keep people in combat.
Comparing feral druids to hunters is like comparing meat to fruit. Both are edible, but both are vastly different in what they give you, and how they effect you, and the people around you.
I can guarantee that Balance requires alot of skill, but so does feral.
Pretty much, for the most mobile caster, go Balance, and for the most mobile melee, go feral.
Balance Pros:
Underestimated (Can open a can of Kick-Ass on underestimater people.)
Mobile (You have roots and cheetah to get away from anything. Don't underestimate it)
Thorns (Crapload of damage to whoever melees you. Can kill a rogue with just thorns if you heal yourself.)
Better spell power compared to ferals (As a Balance druid, you will be focusing on caster based stats. That means you do better spells and heals than a feral.)
(I have never played balance, so I can't assume the cons)
Feral Pros:
Mobile: Most mobile class in the 20-24 bracket. A feral's main form (Cat form) (A feral should never be in their original form unless powershifting or healing/rooting/moonfire), has a 30% speed increase if I remember correctly (That is, if you spec in that talent, which all ferals should do). That means that cat form should do the dirty work, whereas human form should do the heals/moonfire/thorns/root. If you are not in/near a fight, you should be in travel form. You should only be in bear form if you are tanking a dungeon, or being an FC.
Bursty: A feral druid is one bursty son of a biotch. That's no lie. The problem is, though, that you are not invincible. You are melee, remember that. You have to get up and at 'em. Healers can be tricky without help. A pro feral druid should win against anybody below his skill level. People at your skill level, or above, in most classes, can beat you, sometimes. You may be slightly OP, but people can kill you if they are patient.
Thorns: Thorns pretty much, is destruction. Best way to use thorns, IMO, is to put thorns up, go into cat form, and mangle the heck out of the enemy. Most people aren't that aware, and thorns combined with mangle is a deadly combination. If you are FCing, you could play it safe, or do what I just said a few seconds ago (thorns + mangle). To play it safe as an FC, you thorn yourself, pop up a heal, and either go bear and heal if necessary, or go cat, or travel, and run.
Anti-Hunter: Your increased speed, and your ability to decrease speed (If you spec correctly), should allow you to destroy hunters. I feel that if it is group vs group, as a feral, you should focus on the enemy hunters. Most cannot kite you, thankfully. You have to worry about the good hunters. The huntards (Bad hunters), will most likely keep auto attack when you get in melee.

Guess what. Thorns + mangle.
Feral Cons
Terrible spell power: Not the best heals, but hey, atleast it works well with thorns.

You should never rely on offensive spells (Spells that do damage). The only one you should rely on is moonfire, it keeps people in combat, so that pesky rogue can't get away. Even better if you use it on a 24. You'll either kill him (Assuming he's low on health since he's running), or people will notice and kill him. Pretty much, try to rely on someone else for healing if you can.
Smart people can counter you: If someone is smart enough, they might be able to beat you easily. Ferals rely heavily on their speed and burst. We're useless if we cannot get to the enemy (That's unlikely, but some people know how to kite a feral.) Be careful, though. If you can't beat somebody, you have the speed to go away. You can powershift out of snares.
Feral Druids are fragile: We may be bursty, but we are fragile. Don't forget that. We can easily beat one person, maybe easily beat two or three, but we lose health fast. Cat feral druids are meant to be played aggressively, and by aggressively, I mean that we want to pull off as much damage as we can before we die, or run. All it takes is one bad battle and your health will be low, and in the BGs, you are a sitting duck because our heals are slow (HoT and casted heals). It is up to you on how you play, but the way I see it, the most potential out of a feral druid is through aggressive play. Charge right in it. Tear 'em up. I play aggressively, but with strategy.
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Now, here's a pro for both. We can choose our own battles. Both feral and Balance have Cat form. We both have prowl. What does that mean? We can stealth. We can choose who we fight. Remember that. It may be simple, but remember that nobody can see us if we are stealthed. We can see them. We have the time and the safety to determine who to fight, who's what class, and all that.
I'd pick Feral, but I can guarantee that Balance is good, and fun too, if you enjoy casters.