As stated, the mana value of the card is 9. However, when it's on the stack, it's a spell, and that spell has a mana value of 1/2/6, depending on the option chosen when casting.
This is to add to Hackworth's excellent reply, I know that you asked for the mana value of the card, and Hackworth answered that perfectly, but some players unfamiliar with split cards and mana values don't realise that spells and cards are different items for the game to recognise. This is particularly important given that a huge amount of cards that care about mana value want the spell's mana value; others want the card's!
(I would have added this to Hackworth's answer, but I don't have 50 reputation to do so, I'm afraid. )