I have a watched all arrow and flash episodes.
Obviously arrow is better. Flash's characters are less interesting. I like their wheelchair bound boss and the Mexican (?) tech guy. The girl is s bit of a tight ass and not in a great way and the flash himself is a bit of a penis. Moreover, the show is all full of inescapable inconsistencies. Really, a guy who can essentially slow time would never lose a fight, but he does often. Also stuff like if you hit this guy at Mach 1.2 you take him out but any slower and you will die, it is stupid shit.
Arrow is cheesy of course but more believable, and the characters are better. Basically all of them are awesome except for the state attorney ex girlfriend.
Oliver is good, felicity smoke is awesome, diggle is good, slade is a total boss, Oliver's sister is hot, pretty lips (Malcolm Merlin) is awesome. The whole show is ridiculous but very entertaining.