My own suite of quality of life mods that I always use, so I don't have to activate each one whenever I start a new game.
Mods introducing new content into the game.
Transportation of the player, be it vehicles or teleporters.
Augmented or new ways of transporting materials - belts, inserters, pipes!
Trains are great, but what if they could do even more?
Armors or armor equipment.
Things related to oil and other fluids.