Best Evolving System Link + core combinations for training?

So at the moment I'm really enjoying how hilarious it is to train at Link 3 due to the fact that machine just sucks in all the mobs to one place and dies to my Laser spam. I have a feeling though one of the unlockable cores is simply better. So I'm mainly curious as to what's the best training usage of Evolving System. I already unlocked 3 cores, so I can place up to 6 cores into the system.

I'm still unlocking Links 7-9 since I started playing again this weekend. I heard Link 9 simply isn't worth the effort, not sure about the other links.


I'm guessing the following highest cores would be best, save for the last one:
Monster HP
Drop Rate
Herb
Herb Drop Rate
Monster Population
6th <------- not sure