I've really tried to use other red perks other than assassin, but with the spawn nonsense and constant UAV spam, I'm forced to use assassin on every class.
I could make a very good case for all the red perks.
Quickdraw is for when you're on the offense. Its the difference between life and death quite often when you're on the attack, and the double speed flash throws make them about 1000% more useful. In a game type like KC, it means not only you get the kill, but you get the tag.
Assassin is there for you to avoid death at all costs. Its a no brainer if you're using the assault packages. The problem with assassin is that it literally does NOTHING unless there's a UAV or CUAV in the sky. And thats maybe 30% of the time at best. And there are other ways to deal with UAVs than to hide from them.
Blast Shield is for capping objectives. The first thing anyone will do at a flag being capped is throw a nade on it. Its practically required to be effective at being a flag capper or bomb planter/defuser.
Hardline is good on both the low and high end. Combine it with UAV/CUAV with no 3rd on support and you can keep a near constant radar feed up for your team and down for theirs. Likewise, it with the assists adding up you can get to an EMP before your opponents get their osprey. Then you hold it to ruin their day and turn the tide. Combine it with recon and you'll rack up assists like crazy.
Overkill....well, I'm not the biggest fan of it since the secondaries are pretty good, but if you just HAVE to have some CQC to go with your sniper and an MP won't do, its a good option. Combined with SoH pro, you can be pretty versatile.
So yeah, especially if you primarily play TDM, assassin is VERY good. But so are the rest. The red perks are and always have been the single most important choice you make after your primary weapon.