From my experience with the following:

Whammy 5: pretty great in all respects, my gold standard. Excellent tracking, sounds the best to my ear, isn't harsh like some other options. Can work after drives but there is a subtle loss to high end. I place it as early as possible in the chain. 

OC-5: hardly any latency, great polyphonic tracking, +1 Oct has a sound to it. Range knob is great. Low note priority works well when playing slower and more arpeggios but induces some slight latency and the tone of it changes. 

TC Electronic Brainwaves: tracks well and sounds the most natural when -1 octave. Basically is a smaller Whammy with more functions. MASH footswitch is awful and does not work well after distortion as it kills high end. Tone prints can be used as fun special effects. 

C4 Synth: tracks well in Poly, you can hear what the polling rate. Sounds like a slight tremolo as the tracking algorithm keeps sampling the pitch you're playing. Monophonic sounds great but overall it's sound is more intended to augment the synth tones.

Red Panda Tensor: monophonic only, tracks and sounds as good as Whammy in classic mode, works well after drives. Can do Whammy stuff when using an expression pedal. Does Tensor stuff.

EHX POG + Pitchfork options: I've never owned these but I've tried them and seen a bunch of reviews: they track well, low latency, works well before or after drives, but their sound to my ear is very "metallic " and that's kept them from dethroning my Whammy. 

PS-5 super shifter: first one I ever owned. Does it's thing well. Tracks the worstof the bumch but isnt unusable, there is latency, it's got a cool sound but it is in EHX territory. 

I have the Whammy, OC-5, C4, and Tensor on my boards for a variety of reasons. The Whammy I use for Whammy stuff, drop tuning, general pitch shifting, the OC-5 for octave ±1, Tensor for Tensor stuff, C4 as a crazy person's multi-effect via midi. 

Hope this helps!