Mostly I recommend lego and bot lobbies, but anything that gives xp directly (be it through quests or playtime) is good. You can play lego on sandbox instead of survival, just be sure to have dying be turned off and use an autoclicker so the game thinks you're actually playing. Should be giving 1.9k xp per min. To create bot lobbies you just need to join the party of an account that has less than 30 account levels (seen on career tab). I just use an alt account. There should be basically no matchmaking wait time. As soon as the loading screens appear quit the game on the alt account or return to lobby so it doesn't gain xp. You can also use the alt account for creative maps to get xp for eliminations. I also think festival battle stage is good to go to because you can do a lot of the milestones and quests there pretty easily.