Depends on what the other obligatory spellcaster class will be. But so far the Witch Doctor has my interest as being an unique take on a new class.
Main things of interests are the debuffs and interesting attacks with side effects instead of just being plain direct damage spells in various elemental flavors.
Now that I think about it, the Witch Doctor reminds me of the Ritualist from Guild Wars, whom also would compete with the necromancer in the summoning buisness. And I played the ritualist a lot, found it a lot more interesting and flexible class than the necromancer.
I actually am planning on it, unless the necro is brought back. It's unlikely that the necro will be back though. I think the WD is a pretty cool concept, and he may be a worthy successor to the Necromancer.
I am definately going to go with a witch doctor first with so many people complaining I'm sure blizzard will make him powerful. The ability to cast spells on pets sold me. I will spend the next little while thinking of names. I love "Jungle Hobo" but I doubt is will stick around now. My big fear is that they will market the game in only one language and I'll be stuck trying to play the korean version until I can get a family member or business with no scruples to send me one. My dream is it comes with English as a default on every game. I may have to buy an new computer as well, I'm waiting for the system requirements, but that is a pretty small matter as I will need one for Fallout 3 as well.
Really can't comment off just Barb vs WD. Most likely I will be playing three games at once - my own single player, a LAN with my brother, and battle.net with some other friends and randoms - so I'll grab as many classes as I can and just roll with it in some insane frenzy of constant Diablo III fanaticism.