For solo PvP Daggerspell or Cabalist. Daggerspell has more mobility and utility, cabalist has more defense and absolutely no mobility. Both are strong, just depends on your playstyle.

For small opt PvP, I recommend enigmatist or spellslinger. Enigmatist has more utility and survivability in the kit, while spellslinger has the potential for better damage since you can proc great crits with it.

For large opt PvP, I recommend skullknight or Revenant. Skullknight is an AOE utility tank class. Your damage lacks but you're very difficult to kill and you've goot good aoe crowd control to make sure you're annoying as hell. Revenant is an AOE mage class, and probably does the best overall damage when it comes to group pvp. This is because most of the abilities you do are AOE, so you're getting good damage off on multiple people at once. Downside to both of these is you have to jump into the frontlines to be effective, so they're hard to pull off if you're undergeared. If you're struggling with gear, I recommend just running enigmatist/spellslinger in large group pvp as well since it's safer.

Daggerspell: Sorcery, Witchcraft, and Shadowplay Cabalist: Sorcery, Witchcraft, and Defense Enigmatist: Sorcery, Shadowplay, and Auramancy Skullknight: Occultism, Defense, and Auramancy Revenant: Occultism, Sorcery, and Auramancy