I am impressed that no one recommended Frost DKs as well, in regards of spec complexity and how easy it is to kill someone in an arena.
I'd suggest wholol's list however, mainly not because they are easy to play (most specs are now) but because they simply are good in PvP, unlike others, like the Frost DK that I mentioned, who lack utility and are designed only with PvE in mind.
A Fury Warrior or a Retri Paladin isn't easier than say an Assassination Rogue or an Enhancement Shaman nowadays, they simply have solid strong utility tools with straightforward uses.
Since you started as a Havoc, I mostly play Havoc too in Legion, and although it is the most fun spec I've played, it is frustrating in PvP; Havoc feels exceptionally good in BGs, very strong in 2v2, especially with the right PvP talents, but weak in 3v3.
That being said, it is very fun in BGs and it is very satisfying when you manage to escape from tough situations or use Eye of Leotheras on that annoying warlock in the backline and watch them die from their own spells.