Forerunners are definitely the strongest since they made the halo rings -.-
Elites are the strongest warriors. They give spartans a hard time :|
I prefer to use spartans simply because you can change the way they look
Yes, 2 easy but "new" challenges, same with the hard ones.
For the weekly ones, make them in-game dynamic, like a counter on your HUD etc.
Eg, for todays challenge, you could've pressurized players by adding a countdown timer
I was thinking, since I have already seen and done most of the daily challenges, they are beginning to bore me and are no longer challenging.
So, I recommend that more interesting challenges are implemented.
Eg:
Get a multikill on 4 elites or more in firefight matchmaking today - 1800 cR
Destroy 20 phantom guns today in firefight matchmaking - 3000 cR"
Get two exterminations in matchmaking today - 2100 cR"
etc...
I ultimately believe "renewing" the challenges set is a good idea, because they are simply becoming pretty boring.