Back in the days when few amps could produce high-gain distortion out of the box, i.e., the 1980s, I relied on a ProCo Rat (the original version 1) as my main source of distortion. The same pedal that was used by Jeff Beck, Metallica, and a number of other blokes. I'm almost ashamed to admit that its distortion actually sounded better than some pretty decent (and expensive) amps back then, at least for hard rock/metal purposes. I'm glad that I haven't needed that pedal since the 1980s. Not that there was anything wrong with it, I just prefer sweet, rich and full tube preamp gain.
That said, I am using an OD pedal with my Mark V: the Visual Sound Route 66. So am I not happy with how my Mark V sounds? Of course I am! The way I see it the Visual Sound pedal is just an extra that provides me with even more sonic options on tap.
The Route 66 is actually a combo pedal: it combines the Visual Sound Route 808 which is, obviously enough, a Tube Screamer derivative (but with a twist), and a the Visual Sound Comp 66 compressor. The cool part is that both functions have separate on/off footswitches so you can choose to use just one or the other or both (or neither).
The overdrive section is basically a very faithful replica of Ibanez TS-808, but it has an extra function for people who are not so keen on the high-mid emphasis of the original TS-808: a switchable bass boost. So you can use the OD section as a TS clone or a bassier version of the TS. The compressor is very neutral and transparent enough and gives you tons of sustain - but it also has a tone control for those who want one. Again, the tone control can be separately switched on or off depending on whether you want a neutral compressor.
This combination of pedals makes a lot of sense to me. And there are so many ways I can use it! Add some Tube Screamer overdrive to the clean channel for instant blues. Boost the 'Marshall modes' on channel into metal/hard rock distortion with the TS overdrive. Tighten up and give an edge to your channel 2 / channel 3 high-gain rhythms with the TS. Make your channel 3 legato leads more liquidy with the compressor. Etc, etc. I especially like that, with this pedal, I can dial my Mark V preamp Gain pretty low - if I need more gain/compression/sustain, I can kick in this pedal.
The downside: the pedal is manufactured in China. It looks and feels sturdy enough, and has never let me down so far, but it is noisy as h*ll. Hissss, hissss. In a rehearsal, my bandmates are always asking "Where's that hiss coming from?" "Umm, from my Visual Sound pedal." That actually isn't too bad when playing live (the hiss drowns easily in your band's music and general noise) but this pedal is not something I would take with me into a studio.
The Route 66 is currently the only pedal in my regular live pedalboard in addition to a delay pedal (and the Mark V floor controller, obviously).
I still have the Rat (although it is in a pretty bad shape due heavy gigging - it works 100% but looks terrible). Maybe I should try it with the Mk V, just for laughs?