Clueless it's not hard.. go HardCore DOM or KC/TDM .. You can get easy 15-20 kills .. in 10 runs you have the patch.. no gun game or camping or other skills.
Indeed maybe the 1st game and 2nd can be painfull but after you learn.. it's easy.
Marathon, Steady Aim, Agilty.. maybe Scavanger, Faster reload ..
Ghillie suit it's harder.. there you need to have a little skill whit sniper and beyond this you need time.. it's not like you can be a mainac and can get 850 kills in one day. And Clueless you can get in one-two hours .. ok three!
With sniper with 30 kills/match you still need 30 runs.. 10 minutes/run.. = +5 hours. Anyway 30 kills with the sniper it's not easy. So.. Dunno what's harder.. Anyway.. not Clueless!