Ok I will go ahead and admit that many of the perks mention here are pointless in the normal multiplayer. Some of them are decidedly better in Hardcore. I will list the ones mentioned and then argue why I see Scrambler to be the most useless.
One Man Army. - Can easily be combined with 2 things. Weapons that you always seem to run out of ammo on, but that you don't feel you want to leave a perch to scavenge for. A really bad sniper for example that hasn't been discovered but somehow ran through a ton of ammo and needs to get a whole new set of mags. The second thing you can do is run two One man army classes. One with hardline and one without. This let's you swap between them to get additional kill streaks.
Hardline - Good only if you follow the above plan, or if you really feel that one more kill is unattainable.
Sitrep - Not a great perk in normal, but in hardcore is a great substitute for ninja. If there is someone running claymores on the other team then you now know exactly where the enemy is camping/spawning if they are not running around.
Commando - If you still haven't encountered a good knife build I am very surprised, but I will explain anyway. Combine this with marathon, lightweight, and the tactical knife attachment for pistols and sprint around the map going to town. This build doesn't work in hardcore where weapons kill faster, but substitute lightweight for cold blooded and then grab a riot shield and having that extra distance on what is a one hit kill in hardcore is very nice.
