what is best to kill for get good experience for melee
I do now Dark beast
donot have any super weapons doing it with Elder rune weapon and armor
need 5 more levels to go 2 strenght and 3 attack
My preferred way of training combat is through slayer, because that gives you variety and it seems like less of a grind. However, slayer is best when you're prepared to match your combat style to the weakness of the particular assignment. Your example of dark beasts, which are weak to range, and bolts in particular, may not be the most efficient for you for training melee.
Aside from slayer, I've always used the philosophy of "Train on whatever you want", as long as there are enough of them that you don’t have to stand around waiting for a respawn, and they aren’t so far above your level that you need a ton of food or pots to kill one. Pick something that is weak to melee, and that has drops you might be interested in either for selling for cash, or saving for training other skills, such as charms for summoning.
Abyssal demons are one of my favorites for melee training.