I prefer 12-3 over 12-5. Quick and easy, 3 guaranteed chests with 2 more likely.

I do 13-4 now though. still 3 guaranteed chests, but the extra 2 aren't as easy to get as 12-3. It compensates for less chests by having a much better raid boss though.

Currently I already gone to 5 Campaign missions(just starting level 6). Should I do 2-1 or use other missions?