Actually two different bamboo have two different thickness, strength or length between the nodes. To have an even strength you need to use the same bamboo.
Get one with biggest diameter you can get and split them in two, then shave them down to size. However like everyone said, there is a huge variety of bamboo. Like in my country we got different types....some for food, utensil grade, furniture, blowpipe and bow.
In short....get two pieces from one bamboo and get the thickest and largest diameter bamboo you can find. You might not be able to get the best type for bow but it will be good enough.
Avoid ones with insect holes in them. Leave the nodes as the end part as they resist splitting. As for the species, I really can't help you. You can only get the best bamboo by harvesting and curing them yourself.
EDIT: The bigger diameter and thicker bamboo is fairly straight so you don't have to worry about problem with tapering or bending. A big bamboo strip section is also much flatter than a small one.
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Btw....anyone here from cold countries have problems with bamboo in freezing temperature? My old music teacher had problem when he does shows oversea because some of his instruments made from bamboo cracked in cold weather. We've discussed on materials to make the instruments and always have problem with tropical wood getting damaged in different environment.