What are the most valuable promoters and which ones should you enhance and promote first gear, chip..

Get everything to five star first just so you can beat a few floors on each ones ruins challenge. When you're ready to start promoting past five stars, gears give the best boost per level so upgrade the two that have the atk boost for the troop you want to use. Chips don't give as high a boost and they are cheaper to upgrade but there are more than them so the boost will stack, as will the cost (you can get promoters from the ruins shop). Modules give a boost nearly equal to gears if you have all slots unlocked (which you won't until lv34). It will cost more materials than gears though and though you can get the promoters from the pit shop, you can't get as many so it's slow.

So to sum up, gears are probably best but you will need to get the materials from boxes, quests or special event shops. Chips are ok but you can buy some materials everyday if you are earning ruins coins so you'll probably level them up faster Modules are good but you don't unlock all the slots until you're in your 30s and collecting the materials can be slow. Cubes are whatever, you should upgrade them last.

Lastly, you'll get a fair amount of gear promotor 1 from running lairs, these can be converted into enhance material in your bag which is handy for leveling up your gears once you have promoted them