Always, always, ALWAYS max collectors FIRST. Lost time? "I can raid more!"? Other excuses?
Freeeeeeee loot. Forever. They pay for themselves, hardly a setback of lost builder time. In reality, if someone wants into your base to take your loot, they are gonna get it.
Defenses can wait. Loot first!
I pretty much started new th with upgrading collectors and later maxing dark elixir drills. After that its free loot. Hmm with 6 lvl 11 collectors, i make 157,68 million gold & elixir resources/year or 13+ million/month. How much resources you want to lose by delaying their upgrades?
I didn't finish upgrading my mines/collectors until I was on my way to TH9. Up until then, I had no problems keeping 5 builders busy so I wasn't going to stick around just to upgrade those.
Assuming level 12 collectors will have a 5 day build time, it will take 70 days to upgrade them all if I dedicate one builder to them. Since I'm less than 3 months away from maxing TH10 defenses/lab, I probably won't do many of them until defenses are maxed, unless level 12 collectors produce 4000+ per hour.
I have all LvL 7 collectors/pumps and I manage to get 200-300 attacks in per season and constantly have my lab upgrading and all 5 builders at work. It all depends whether you're a collector sitter or not.
This is why I keep saying an achievement needs to be tied to collector levels to encourage people to upgrade them.
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