The answer is almost always Mage. Frost is in good shape. I got surprised yesterday by a level 60 mob when I was 51 and I came out the winner, so I’ve got no complaints.
Pure easiest class is havoc DH. you can boil it down to a no more than 6 button rotation even less with the right talents. I learnt how to play it with a broken hand when BM was unmanageable, i was able to stay competitive for my ilvl
I like my Assassination Rogue, she feels pretty easy to play now. It depends on what you like - for me I play a lot of multi-dot classes so those are the easier ones. I just played Shadow and Feral but Assassination feels both stronger, has one upkeep less than Feral, and gets much better CC.
And IMO any healer except Disc (strangely) if you have great DPS players in your group.
It’s pretty nice, you just do dot dot dot, stab, special dot, powerup, stab, dot dot, stab, dot dot, stab, and so on
There’s a little more intricacy that you can totally ignore if you’re doing like 12 or heroic raid for example. Just stun prio targets, get your dots out and honestly grab a cup of coffee