You could use e.g. Diluc, Mona, Diona and Sucrose to cover a lot of the fundamentals.
Diluc provides pyro and a claymore. Pyro is needed for vaporize with Mona and melt with diona, the claymore is useful for breaking geo shields.
Diona consolidates healer, shielder and cryo support and enables melt reactions.
Mona uses her omen debuffs to lower enemy resistances and also amplifies Diluc's damage with reverse vaporize if needed.
Lastly sucrose provides crowd control and swirl reactions which can lower elemental resistance with the Viridescent venerer artifact set.
This is just a "meta" suggestion.
Honestly you could play anyone and they'll be viable if you invest ressources into them.
Play for fun and choose enjoyable units.