Sharpshooter (ranger) is the easiest to start off with imo. They attack from range and they can normally kill a mob before it reaches them and they can solo fast. In pvp they are fairy easy too just pew pew pew. They can do well with orange and pvp armor sets. Nerco (demon) are probably the hardest to get good at. I played a nerco to lvl 32 (not very far I know) but they are squishy and if a mob attacks first you can lose a big chunk of HP. They need legacy armor so they are not as squishy. In pvp they are challenging too. DarkStalker (assassin) are probably in the middle. I have a lvl 70 darkstalker. They are easy to solo with in pve and can solo bosses with the right gear. Orange and pvp armor sets are the best legacy isn't very good. In pvp they are a bit hard to learn to max their potential however.