I’ve started putting together a sheet that calculates S3 missions like I did for S2 missions, but haven’t got beyond copying the S2 sheet yet 
Eventually. But looking at where they appear to be, I see some possible standout levels:
- S3:1-2 Normal, S3:1-9 Normal, and S3:2-3 Normal have both trolls and boars; I imagine you will get the trolls before you finish the boars if it is like S2 was.
- S3:2-8 Normal has 5 waves; the other boar choices only have 3 waves, so I’d expect it to finish the boar mission fastest, after you get all the trolls you need.
Edit: Missed two of the stages with both missions. Oops. Fixed. Cleaned up and clarified things a bit too.