The idea of the priority list is to ensure that you can perform a higher priority expense as soon as it becomes available; i.e. that it doesn’t get delayed because you spent your coins on a lower priority item.
For example, as you get closer to the next player level, defer upgrading armour and gear so you keep coins in hand for the permanent upgrades and for upgrading your primary and secondary heroes (provided you have the crystals / hero medals)
This is my recommended priority order for spending coins
- The first Permanent Upgrade, Veteran, which gives you a free perk roll at the start of the run
- Getting the Equipment Drop Chance skill for your Farming Hero and levelling him/her up till you can at least regularly reach the 2nd boss on the World lower than your current world.
- Upgrading your main weapon
- Main Heroes (see also Best Hero):
- Skill Tree upgrades if the next skill gives you attack. Rule of thumb is to choose the path that gives all-out attack (i.e. not attack against a specific type of enemy) except for your Farmer where you’d pick the Equipment Drop Chance at 1 Star
- Upgrading / Promoting
- Promoting high priority non-playing heroes to Level 20 / 50 for the All-Hero bonuses (see this for priorities)
- Permanent Upgrades (the reason it’s not higher on the list is because you can’t pick the upgrade and only a few of them (Nimble Hands, Good Shot, Gun Mastery and Gear Mastery are really useful, and even the Gear Mastery is only helpful for fast guns)
- Main Heroes: Skill Tree upgrades where the next skill does not give you attack
- Promoting low priority non-playing heroes to Level 20 / 50 for the All-Hero bonuses
- Upgrading your Gear (see also Best Gear)
- Upgrading your Armour (see also Best Armour)
- Skill Tree for your other heroes - but only if you have enough Rings for your Main heroes’ skills.
If you are generally doing well for coins (buying BP/SBP every month, grinding campaign a lot, prioritising your spend carefully) you could also purchase upgrade material from the merchant