You get two winning strategies:
Lock: You get raid utility, relatively straightforward class (imo) and basically invaluable to a raid team through a lock closet and cookies.
DK: Strong self sufficient tanking and a very powerful and versatile DPS in UHDK.
I’m my opinion I’d go lock and find yourself a guild you can be regular with. Being a DPS is low-stakes and is pretty fun both M+ and raid.