I have MD top 3 ..... 92.5642% (pre nerf) / 91.0460% (current) merc discount is nothing to sneeze at since lets you buy all mercs with just money caches for the most part. MD is basically a 2.777 money multiplier that only affects mercs (obviously).
These lists are always different for everyone due to various reasons like playstyle. I personally ranked them as relative increase when going from Legendary to Insane since some good artis can just stay legendary with no real penalty while others "only" shine at insane. AV could be forever at legendary, and no difference noted while stuff like IM is insane or into the trash it goes tier. Also, I was biased towards artifacts that let me stop using powers since those are finite resources for me.
Note: I had an epic AV + legendary AV + insane AV and tested them on same market for science long ago but can't find the data atm.
Edit: I just noticed ivan ranked TW @ 7 and 10. Made me chuckle.
At the beginning of a level I always swap in the best cache boost or whatever, I'm a little OCD about swapping them in later in the level too. The supercharger army camp I only use for battles. Time Warp for battles and right before super ascending. I don't use any actives for actually clearing levels.