I think it's Burton Albion - League one that has world class training facilities already. Or the likes of Sunderland, Stoke, Forest, Sheff Utd all decent sized club languishing in Championship Other than those, Majority of the lower division teams aren't really primed for long term success.
Charlton Athletic have been my go to team the past few editions. From League 1 to the championship and back again they went. Former premier league and makes for an interesting challenge as they aren't where they used to be financially, stadium wise either.