Subspace easy. I can play Event mode on other Smash games but this one is the Adventure mode now? Hell no. I just want a well done, co op Subspace 2. You don't even need to have tons of cutscenes. Just playing with a friend going through a stage with Sonic and Mario is novel and fun enough.
Subspace had its issues, we get that. But it kills World of Light which is just a glorified event mode. I laughed during Subspace, was genuinely interested by what was going on with some of the characters...the same can't be said for WoL.
How does each improve? Well, make World of Light the Event mode in the next smash. And make Subspace 2 with Nintendo/3rd Party themed worlds with a light story and meaty campaign. While World of Light felt like grindy busy work, Subspace felt like a compliment to the multiplayer focus of Smash.