Dual Boxing : best class to pair with a Demon Hunter?

Hello guys,

I'm sorry if this question has been brought up before, but Google couldn't find anything relevant and recent so I decided to get some advice here.

Basically I main a Demon Hunter (used to be Rogue until Legion pre-patch).
While not interesting in a 3-5+ team, I like the idea of a duo doing content together. Since I'm also interested in doing content like Dungeons and maybe even Raids if it works out fine, I would need another class that could complement my Demon Hunter well.

At first I wanted a melee class, however there are 2 issues : interact with target is wonky and in PvE (especially in instances) there are so many oneshot AoE from bosses and mobs. Even with an Outlaw Rogue which has extended reach for attacks.

basically I have to choose a caster. I've been thinking about it but I simply cannot make up my mind. I tried mage but it's not really my jam, Warlock is cool but lacks movement abilities and I feel will struggle to follow my DH. To sum up :

Shaman Elem
Shadow priest i f it gets good changes for Shadowlands?
Mage, but gameplay felt a bit meh to me
Warlock

I kinda want to go with a Spriest, but I have never played one, some say its fine some say it's boring.

What are you thoughts? Which class(es) would be ok for my goals ?

Thanks and take care everybody !

Consider BM hunter and treat the DH as a pet.

I would go disc priest before shadow.