I've played every characters a considerable amount of time and here is my advice.
Sword Fiona is the safest bet and will earn you the more. She almost always been the highest damage dealer. Higher damage in parties means more loot. It's ridiculous how she changed since season 1. She can be played extremely offensive now. She has insane survivability, a decent dodge(without iframes) and all of her SP skills are useful. So, don't think her as a passive tank character. You have shield deflection to cancel your amaranth kicks into another amaranth kick and enhance their damages even further.
Other than that, Hurk(Greatsword) is a pretty solid choice as well. Again, very high dps and unique abilites like life steal and not dependant on stamina(most improtant one imo). So, you'll be damaging bosses while your friends are wasting their SP or waiting for their stamina fill up. He's also quite easy to play with huge absorb frames on his dodges. Both characters have very offensive playstyle but Hurk might get repetitive with his smash rotations.
These are the prime female and male character i always recommend if you are looking for an easier time in this game. With them you'll still deal decent damage even if you play passive.
Currently, the only hard part about arisha is how unforgiving she is toward lag. Many moves do not function properly when having even a 0.5s delay, because you cannot que them in advance. Characters with can que moves suffer much less so from delay.
Every character is unforgiving towards lag(except pillar karok).
Arisha ain't hard. You go in mana mode and never run out of mana nowdays, friggin ridiculous. She got dodges blocks everything to survive.