Went to finish capping my favor and got every challenge 6 stard. Well every one that is possibly anyways:
22 six star'd (maximum possible for U14):
Disruptor and Shortcuts are broken and impossible to achieve over 3 stars due to simply 100% impossible objectives. (You need to reach impossible levels of rates/upgrades that simply cannot be done even if you were an advanced mililtary android). No one has ever done more then 3 stars even on the lowest CRs. Proof is aval on the official leaderboards, which has zero completions of 4+ stars, but tons at 1-3.
Pic of them at 3 anyways (which is actually kind of hard)
Thus current maximum challenge favor is:
5 PDKs @ 6 a piece = 30 PDK favor
17 Canniths @ 6 a piece = 102 Cannith favor
4 broken canniths @ 3 a piece = 12 Cannith favor
Grand total = 144 favor
Cpl select runs from our 6star-athon I thought were particularly challenging. more to come later:
Ring of Fire - CR30, 6 stars: 911. The toughest challeng combat-wise for sure.
Sunset Ritual - CR30, 6 stars: 290. Also a tough one combat wise, tho a lot easier then the arena, and fun to run, so I run this one a LOT and am very good at it, wont be an easy score to beat, tho it is beatable if your up for some healthy competition.
Epic Lava Caves- Collosal Crystals - CR25, 6 stars, 755. Possiblt the toughest challenge to 6 star because of non-combat reason, the strategy, luck and teamwork required is utterly insane. Im betting we are the only group to ever do this, took an insane amount of effort.
Epic Rushmoors - Moving Targets - CR25, 6 stars - 4973 - A crazy hard challenge and crazy high score considering (ultimate characters making insane use of blitz and other powerful abilities was required). This one took 3 tries iirc due to incredibly poor luck on the boss teleports.