as rip said, before 78 dagger is not worth at all (here is example of how much useless dagger pre-78 can be https://www.youtube.com/watch?time_continue=3&v=-4odNGvhUTY), after 78 PW/AW is still bad even if you get focus death, they become somehow playable if you get hero on them, but yeah, thats 3 people on whole server and you gotta compete with biggest china fishes which are fully stacked and gonna do pretty much everything to get those dagger heroes
currently -
pre-78 it goes like this TH>>AW>PW
past-78 with FD its AW>PW>>>>TH
on future updates - next update i would rate AW > TH/PW, in even further updates i would say TH>AW>PW will be a thing, also daggers get boost in next update we should be getting in next few months, and generally speaking since debuff resists will become more and more common, the meta will be switching from control classes into burst classes, so for example warlord/gladiator/dwarfs are definitely not going to see place in melee cp, rather it will be all about daggers/tyrants/destros (classes which are not dependant on CC)
about leveling, i guess faster and more enjoyable would be to lvl up actually SR/HE and then just class change it into dagger on higher lvls (careful dont pick PR as he cannot class change into daggers)