Which wood species (type) is best for me?

Wood type is all personal preference.  

-Ash-

White Ash was the most popular wood type until the early/mid 2000’s. It is the lightest feeling wood when it comes to swing weight. If you like the feeling of the ball flexing or trampolining off the bat then ash is the wood type for you.

-Maple-

Maple became popular when Barry Bonds broke the home run record.  Maple is a very dense and hard wood. For those transitioning to wood from metal, if you like the feel of composite type bats then you will likely enjoy swinging maple.

-Birch-

Yellow Birch is the newest out of the bunch. Birch is in the middle of the two and share characteristics of Maple (Hardness) and Ash (Flex). It also allows you to be able to use bigger barreled bats while maintaining a good wood density balance.

-Bamboo- 

Bamboo is also a newer choice on the market. Many companies have recently introduced bamboo models. Some bamboo models are used in conjunction with maple (see Composites below). Since bamboo chutes are hollow, they are made by pressing bamboo "strips" into billets, and then the billets are combined and made into bats. Bamboo is an extremely strong wood, with tension strength greater than steel.

Choosing a Wood Bat
In today's game most players using wood bats have previously used aluminum bats. When a player makes the transition from an aluminum bat to a wood bat there are many things to be considered. First you must keep in mind that aluminum bats are hollow and wood bats are solid. This means that even if your wood bat is a minus 3 (length to weight ratio) it will feel much heavier than an aluminum bat that is also a minus 3. For this reason most players choosing a wood bat will need to select a model that is balanced. An evenly balanced bat will feel lighter and be easier to control than an end loaded bat.The balance of a wood bat is determined by two factors: barrel size and handle diameter. Most large barrel wood bats tend to be very end loaded as most of the weight is out in the barrel. This will cause the bat to feel heavy or end loaded. Medium to smaller barrel wood bats tend to be more balanced as the taper from the handle to the barrel is less drastic. This keeps most of the weight near the middle of the bat causing the bat to be more balanced or evenly weighted. Handle diameter will also play a big part in the balance of a wood bat. Bats with thicker handle diameters have more weight displaced throughout the handle of the bat. Taking this weight out of the barrel and shifting it toward the handle will make the bat feel lighter and more balanced. 

Overload/Underload Training

This is an old concept to break Speed barriers. The Overloading increases resistance and thus promotes using the big core muscles and the underload Training allows the Body to move faster than it can normally. It mostly works on neuronal aspects allowing the muscles to fire faster.