I like using lightweight pro (for the quick aim after running) for all my SMG classes since I always run to flank with them.
For my other more stationary shooting classes (like the assault rifle classes), I'll use stopping power depending on how effective it is on the gun.
The biggest pain for me is choosing perks for my sniper class. Sleight of Hand Pro can be a lifesaver, but I'd need Bling for silencer + thermal.