http://minecraft.gamepedia.com/15w37a

Axe attack speed is now based on the type, rather than being exactly 0.8.

Wooden and stone axes have as speed of 0.8.
Iron axes have a speed of 0.9.
Gold and diamond axes have a speed of 1.

Axe attack damage changed.

Stone and diamond axes now deal 9 damage, instead of 8 and 10 respectively.

This makes no sense. A stone axe with a slower speed should do less damage than a diamond axe at a faster speed. The faster the speed the higher the damage.

Also a wooden axe should be faster than a diamond/iron/gold axe as its a lighter material....

What you should do is use a formula of something like this:

Speed x base damage + material bonus = actual damage.

Wood gets no bonus.

The bonus should improve the end result so that the slower axes do more damage than wood. The more dense the material, the heavier it is. So it should swing slower, not faster. Having a wood axe do as much damage as a diamond axe at a cost of speed is retarded. It makes no sense at all.