Re: Stomp boxes or multi-FX?
Pedals have the advantage in that you can mix and match brands - Ibanez Tube Screamer + TC Chorus + BOSS Delay, etc.
With multi-FX units, you either get all of one brand (BOSS/Roland, Digitech, ART) or you get a handful of whatever-the-designers-coveted-that-week (Line6's fanatical devotion to the Toys Of Yesteryear i.e. BigMuff, FuzzFace, etc).
However, all-in-one units are easier to manage - one cable in, one cable out (or two, or four at most), and easier to set up for use (no chasing down patch cables and batteries and wall warts and such, plus your knobs get bumped unless you've got them all in a board).
While you can get one-trick-pony rack units like BOSS's old half-rack stuff, it's easy to end up lugging a 6-space rack with 12 half-rack units in it (OD, Dist, Chorus, Flange, Phaser, Reverb, Delay, etc). As well, not everyone offers their stuff in half-rack, or in single-function, so you might have to settle for a Digitech multi-FX full-space unit just for the selection of delays and reverbs, a half-rack BOSS Chorus, and a 2-space vintage rackmounted flanger made by a long-dead company, for example.
Then there's the question of wah and/or volume pedal. You can get a Crybaby in a rack with an expression pedal, or an all-in-one unit like the 1101 with an external CC pedal (ART X-15, Digitech ControlOne, etc), but then if it's not the pedal made for the system, you have to program CCs.
Rack units also have the advantage of multiple settings available at the push of a button, whereas most pedals have either on or off, with a relative few offering programmability. Of those, most require either a tap-dance ( Digitech's old 2-button pedals where you have to go into Bank Select mode and the pedals selected up one or down one, or you only get step up/down, so you have to know how many steps it takes to get where you're going, and if you miss....)
But then, that scenario really only applies if you're doing a ton of covers that require different flangers or phasers (VH, Pink Floyd, Alice Cooper, etc).
For me, the single-brand multi-FX units like Digitech have been worth the flexibility tradeoff. I may not have the best of any given effect, but I have enough variety through multiple presets that I can get the sounds I want quickly and easily.
It doesn't hurt that many of those older units can now be had for under $200 regularly, like the GSP 21/Legend, or the TSR-12, so not only can I have all the User presets I can stomach, I can do things a single unit can't do, like Flanger on the left and Phaser on the right, or slapback delay on one side with a gated reverb on the other, or a Gated Phased Reverb mixed with a Gated Flanged Reverb.
And all for a fraction of the cost of an Axe-FX.
