Does anyone know if there is an equal chance of getting any type of legendary or is there a set chance for each prefix? (Prefix as in Wounding, Powerful, etc)
According to NukaPedia there is no set chance of a certain type of legendary weapon dropping. Legendary weapons are only able to be found on the bodies of "Legendary" variants of enemies and the type of enemy doesn't effect what weapon you'll get. e.g. A Legendary Glowing Radroach could drop a Furious Pipe Rifle, or a Never Ending Assault Rifle.
After all, I'm only paraphrasing the wiki, more info can be found on NukaPedia.