[Saulot]

That's not quite correct. A water bless gives you 1.5 X whatever amount of attacks you already have. A fire bless does not confer 2 attacks a round unless the creature already possesses 2 attacks a round.
So with the water bless if you have 2, you're getting 4 on every other turn. Since each attack is at a -2 defense to protect against, whenever a creature attacks 4 times, the attacks will essentially be at +0, +2, +4, +6.
This is even more so the case with 3 attack sacred creatures. Though I don't believe there are more than a few of those.
To summarize a 2 attack creature with fire bless would have attacks at +4, +6 (over it's standard attack value) every turn. Whereas a 2 attack creature with water bless would have attacks at +0, +2 one round AND at +0, +2, +4, +6 the second round. If you consider them that way, the water bless is much worse attackwise on half the rounds, and a little better on the other half.

Furthermore, water 9 also gives 4 defense, which depending on the creature is a very serious difference in survival. Generally speaking, it is more important for your troops to be hard to kill, and moderate at killing, than the reverse.

The movement speed boost is not to be ignored either.

Upon some reflection this is somewhat comparing the wrong things, since the comparison should be between the strong fire bless (6ap fire attack) vs. the strong water bless (50% quickness), seperately from the +4 attack, vs +4 defense.

I will however, not state that any one is 'THE' best. That's purely a judgement call, and such things are never facts.