OVERDRIVE- The very best of the best ...pick one!!!

OVERDRIVE DILEMMA

It is an OD world. Even those that play clean usually have a tube amp or some digital black box to imitate one.

A tube amp even the cleanest by the very nature of the tubes produces second harmonic distortion.
Second harmonic distortion means it exaggerates the level of the harmonic that is the same as the note that is being produced. In short an 'A' note has loud 'A' overtones a 'G' has loud 'G' overtones etc.
A low gain/transparent drive attempts to do this.. Unfortunately most work better if they produces more then just the second harmonic on purpose since just producing the second harmonic is tricky. You get an uneven sound when either the the harmonics dropout or come in at random. In short the tone is inconsistem fro moment to moment.  Analog tech is like that. Imperfect! LOL
Very very few big name pro's use solid state ( basically transistor) amps. Digital modeling yes ...but NOT a standard solid state amp.
You can rationalize all you want but things like the Quilter do not cut it unless you never have a good medium gain or high gain OD on all the time.

TYPES OF OVERDRIVES
Lately life has become easier by calling all dirt boxes an OD. One just labels what type.
Then names speak for themselves.
Transparent OD's are OD's that let the type and character of the guitar come through.
High Gain pedals have been & some still are called Distortions.
A Fuzz really is not an OD but some have adopted circuits that make them a hybrid.

LOW GAIN
MEDIUM GAIN
HIGH GAIN
METAL
VARIABLE
FUZZ Hybrid

As a rule of thumb Fender guitars benefit more from a transparent drive. Strats in particular. Without the Strat's 'chime' getting through a Strat is not a Strat. The PU's can easily end up sounding like  thin and cheap sounding Humbuckers. Nasty!!!

BRIT OR AMERICAN VOICED OD'S
The voice of an OD is usually based on Marshall or Fender amp types.
the exception is Metal or Fuzz hybrids that are so distorted that a $200.00 guitar in a blindfold test can sound damn good. lol

The identity of the sound is really about the sound of the power amp tubes. Fender uses 6L6 or 6V6 tubes and Marshall EL34 or EL84 tubes. Marshall has fat mids and tends to distort easier and Fender tends to be cleaner and scooped.

FENDER 
Fender is damn hard to emulate and requires much more detail in the sound. Marshall is so forgiving that a few $30.00 Chinese OD's actually sound pretty good!
The most bullet proof OD's are the better Marshall-amp-in box OD's some are variable gain which gives you a damn good sound from near low gain through to high gain.

The only reasonable convincing Fender type box I have heard is a Free the Tone String Slinger.  It is toted as a Fender black face amp sound. I think they were trying for the sound of a Dumble Steel String Singer ...the name is a give away. lol 

The Dumble amp started life as a Fender Deluxe schematic and went from there.

At $350.00 USD it is a big OUCH! 
It ain't perfect pushed hard you loose's it's Fender character and to me sounds very coarse. But at low gain it is killer!!!

MARSHALL

First if you play a Strat the best hands down is the 
Thermion Heart Breaker.
It lets the Strat chime come through. It has gain control of the pre amp and power amp on separate knobs. You can push the power amp and pull back the preamp and even get a good Hendrix type clean sound. I wouldn't be without one!
At $180.00 USD this pedal is a steal.


This works onStrats, Teles just about any guitar ...but especially those using Humbucking PU's.  Lawrence Petross Designs LPD 87 is bullet proof. No low gain but ....
a nice medium gain right up to 80's Metal.

This is in my opinion is an OD that never fails to impress any player!
When one thinks of a Marshall stack screaming out to you on a
recording of your fav guitarist this is the sound you have in your head!!!
Yes it is a cool $335.00 USD but worth every penny!

DAWNER PRINCE RED ROX DISTORTION
In a blindfold test of 35 of the best OD's the Red Rox won!
The tone knob is set so if you move it into the bass range you get 
a great scooped early Metal sound. At about 1 o'clock you get a nice rich fat mid sound and still further it heads into the late 80's origins of modern Metal.
Even at bedroom levels this sucker comes in first place for a long sustain.
At $220.00 USD it is well worth considering.




OTHERS
If you want a very organic transparent variable gain OD that goes from low gain to the low end of high gain and sounds stellar in all then your 
pedal just has to be the Stormy Monday. It is not meant to copy a 
particular amp.
It is ideal for Blues based music or ...any kind of the Americana genre. Oddly ...used at lower gain it would suit many Jazz players. 
It sounds very, very tube like and is unusually sensitive to the personal expression of your touch.
It's $200.00 USD ...and not overpriced for it's quality in every respect.


CHEAP

Well one does come to mind. The biggest selling ...tube amp sounding ...medium to near high gain OD in history.

The Fulltone OCD. It ain't cheap either lol. 
BUT ...
Mogoo make a clone. Or more to the point ...they make a 
counterfeit copy.
Unfortunately for Fulltone even the circuit is a copy.
The Mogoo is $37.00 USD

Two pics & one is a fake OCD

CONCLUSION
There are many,many other OD's I love and own  but they are perfection to a very specific music or lean more to one's taste. 

Some like buttery smooth OD's some like harsh rip your face off sounds.
The four OD's I have recommended are quite simply the best of what they do.
What they do is cover a generalized category.
They are all based on FET transistors which are the closet you can get to a real tube.
Sorry but the one weak point of any OCD is it's weak sustain. The true test for sustain is playing at 'Bedroom' volumes.If you push out 20 watts or more the amp is loud enough to feedback into your pickups and give you more sustain. 

They have all been posted with video.
So check'em out!