best custom challenge to finish

What is the best custom challenge to finish and get good credits?

250 headshot in 3 hours in matchmaking multiplayer

or

500 medals in 3 hours in griffball

FF:

800 kills in 3 hours (10,000cR)
800 medals in 3 hours (10,000cR)

Matchmaking:
Headshots pay a TON.
I usually do 150 kills (~6,000cR), 200 medals (~8,000cR)

When I do matchmaking custom challenges, I pair headshots with kills. From what I’ve seen 360 headshots will give the maximum 30,000 credits. Kills are worth about half as much as headshots for 15,000 and change. Throw in a challenge for wins and you can get 50,000 in a good SWAT session. That’s if you’re looking at just from a “big picture” perspective.

What I usually do is 100 headshots/kills in 3 hours. Turn those in and repeat. Over the same 3 hours or just a little more you can squeeze out a few more than the 50,000 credits above.

And as someone mentioned above, 800 FF kills and 800 FF medals each give the max 10,000 credits. You can turn those over pretty quick.

Edit:
I checked back on history.
100 MM headshots in 3 hrs = 8,498 credits.
100 MM kills 3 hrs = 4,249 credits.
Total = 12,747 credits.

Do that 3 times (you should be able to get 100 headshots in an hour in SWAT) = 38,241 credits.