I love the Tracker sight. Easy to see people at long range (not running Incog) but the real benefit is switching the sight and having amazing iron sights on every gun. I typically run the irons normally then ADS, flip up the tracker, scan the area, flip down the tracker and move on. The other sights in this game have weird reflections and look dirty a lot of the times so I don't use them. The holo sight on Overlord for instance is useless in a lot of places.
I liked the Target Finder on LMGs in BlOps2 when I could post up and lock down an area but not on anything else. Too tight of a view and the zoom in was a little too long for my tastes. The MMS with the no zoom was actually my preferred sight mainly for the clean sight picture, and the fact that it didn't zoom in at all. The see through walls randomly (which didn't always work anyway) was just a bonus.
"Cover your receptors Perceptor." Driver picks the music. Shotgun shuts his cakehole.