For me it's probably the PartyScreenEnhancements and the RTS camera. The first one ads just a few buttons that let you halve the time you spend in the menus doing basic stuff like upgrading troops, the other one is a dramatic improvement to battles as it allows you to both pause the game and use an RTS-type camera to observe the batttle from the sky, which in combination let you actually order troops around during battles AND fight in them at the same time without insane micromanagement.