Today, my rack is relatively simple, compared to what it used to be. It includes a Fractal Audio Axe-FX II and two Roland synthesizers: a GR-55 and a Fantom-XR (see the physical wiring diagrams on the right).
In terms of effect processors, once you get an Axe-FX, you can pretty much ditch everything else, including your amplifiers. Within a 2U rack format, you get state-of-the-art effects and amp simulation. 15 years ago, my rack was 6 units high and weighted tens of kilos. You could see a Mesa-Boogie Triaxis for preamplification, a 50/50 (also by Mesa-Boogie) for power amplification, all that connected to 2 Marshall cabinets. In terms of effects, I had alternatively a Digitech TSR-24s, a Lexicon MPX-G2, and a Digitech DHP-33 for harmonization.
The Axe-FX takes a third of the equivalent rack space, offers effects and routing capabilities that outrank everything else, and what's more, you are no more enslaved to one specific, big and heavy (pre)amplification configuration. The Axe-FX doesn't do MIDI conversion and won't replace a real synth either, but maybe this will change in the future...
As a big fan of Uzeb, I have always been fascinated with the possibilities offered by synth access to guitarists. My first guitar synth was a Roland GR-50. After that, I explored more evolved solutions mandating the use of different devices for guitar/MIDI conversion and for synthesis. One of my last configs included a Yamaha G50 for conversion (a model of what should not be done in terms of design) and a Roland JV-1080 as the sound module.
I eventually turned to the GR-55 for several reasons. First of all, it sort of gets back to the original idea of the GR-50: a compact solution integrating both guitar/MIDI conversion and sound synthesis, all of that in a much more recent, and hence performant device. The guitar/MIDI conversion is probably one of the best so far. Also, it is possible to save 10 different settings for 10 different guitars, something convenient for me who already uses 7 of them (those settings are known to be absolutely crucial for a good tracking).
But there is also another very important factor in that choice: again, it's flexibility. The problem with rack-based solutions is their bulkiness, especially when you just go jamming. From that perspective, the GR-55 is interesting because it is not only a guitar synth. It is also an effects processor and an amp simulator in a floorboard version. Of course, it can't compete with the Axe-FX, but just for jamming, it's more than enough (no need for carrying heavy amps either). Consequently, I use it alternately as an ultra-portable floor-based standalone solution, and rack-mounted for more serious applications.
The Fantom-XR is mostly legacy from my previous configuration (it may disappear someday) but I still have different uses for those two pieces of gear. The GR-55 is essentially used as a "lead" synth, of equal importance with the guitar. In fact, its audio output is injected into input 2 of the Axe-FX so as to be able to combine the guitar and synth sounds, and for example apply effects to both of them (the final reverb, typically). It also lets me use the GR-55's COSM technology to create virtual guitars (sitar, open-tuning etc.) and plug them into the Axe-FX. On the other hand, the Fantom-XR serves as a distinct instrument, with its own audio output, for synth waves, layers, special effects, sequences etc.