Personally I think the perks in order from most useless to most usefull would be something like this- (third) scrambler last stand steady aim commando sitrep ninja (second) hardline danger close lightweight stopping power and cold blooded are about the same (first) scavenger bling one man army marathon sleight of hand
Now I'm gonna give reasons for ordering them that way starting with the most argued
First of all I think that all perks a situational and my thoughts of the most usefull perks are based on how I play
sitrep: everybody trashes stitrep and says it's on of the most useless perks but I that people just don't use it right, spessifically the pro is very usefull IF you pay attention to sounds as well as sights.
Hardline: personally I play core so I never use hardline over stopping power considdering I would rather be actually able to get three kills for a Uav instead of requiring on less kill that I could get with stopping power while I may get one with hardline
bling: I say bling I realativly useless because most people just use one of the attachments to replace the sights which is pointless because you ahold be able to use the iron sights on your favorite guns though I can understand replacing m16 sights also people use it to put silencer and fmj because they don't understand that the little bars in the create a class menu lie and fmj only helps damage when using bullet penatration
lightweight: lightweight is a very strictly situational perk and only helps for rushing and close quarters combat if you have pro