A DK will cover everything fine. Anything will cover you fine. The one disadvantage of a DK is that it doesn’t have any speed-up abilities, and when you’re soloing a looooong instance like Siege of Orgrimmar or Hellfire Citadel, you do feel it.
If you’re doing DK, have a look at a Frost offcpec, which will give you more ranged reach and casual AoE when you don’t need tank survivability, which is to say 97% of the time.
Just to mischievously throw another complication at your choice, if you’re farming old instances, you really should also consider your mog collection. I don’t know how long you have been gone, but the game now allows you to transmogrify your gear, to take on the appearance of any gear you have earned. If you are interested in this, check out the available armour sets for the classes you are considering: https://www.wowhead.com/transmog
Gameplay is pretty dead in this patch. If you want a current class for group play, I don’t know what to tell you. Clicking around https://raider.io/ will give you a good sense of the popularity of the classes and specs for Mythic+ Dungeons and Raids.
The Horde/Alliance ratio is crazy skewed now. The overall population is abiut 3:2 in favour of Horde, and - more signiicant - the Horde side is much more active, so the effective difference is even larger. Blizzard have enabled cross-faction groups for instances, so this effect MAY subside in Dragonflight, but I wouldn’t bet on it. So if you like Horde, go for Horde!
Crafting Professions - uuuurrrggh. Professions are not what they were. Blizzard has been waging a war on them since … Warlords? definitely Legion … and have beaten them to a bloody pulp. They have already destroyed the low-hanging fruit. First Aid has been removed entirely, Archaeology was removed “for” Shadowlands, and may not be coming back. Inscription has been reduced almost entirely to cosmetics. The problem is Mythic-Plus. M+ introduced a new plentiful source of gear, and Blizzard don’t want Professions competing with that.
Blizzard SAY that they are bringing back crafting professions in Dragonflight. Colour me dubious. They SAID that they were refreshing professions in Legion, when they actually nuked them.
I went through a minor AH Goblin phase once, so while not an expert, I do have some familiarity with making gold. I would not like to be relying on professions for gold these days.
P.S. Again, because I don’t know how long you have been gone, I should add that the WoW Token has entirely corrupted the whole concept of earning gold. When you can buy 300,000+ gold for the equivalent a month’s gametime, you have to be making a lot of it to be worth spending time making gold.