Which level 7 creature is the best, and why?

Azure is the best

They are level 10:p

The Archangel will defeat the Black Dragon because it moves first, and its stats, except for HP, are higher than the Black Dragon's. The Behemoth will defeat any melee unit because it reduces defense. The Hydra is not for duels, but for eliminating several groups of enemies. The Titan loses to flying/teleporting units, but it kills both the Behemoth and the Hydra because they are slow. The Black Dragon and the Gold Dragon with antimagic are good on one hand, but it can be very frustrating when they cannot be healed, resurrected, or even have a Bloodlust spell cast on them. Also, don't forget about the morale boost from Angels and the luck reduction from Devils – these are team fighters, after all. Phoenixes are effective due to their growth and regeneration, but this doesn't always help; at least they have high speed. In my opinion, the worst are the Ghost Dragons; if they don't get a good aging buff (which happens rarely), then even a regular Angel/Devil will defeat them.
The outcome of the battle depends on the combat situation, but I voted for the Gold Dragon because dragons are cool.

Added 1 minute ago
By the way, why are there only 7 options in the poll out of 9? o_O