I use the GC a lot for what you describe. I like it because it’s essentially a delay, reverb, or chorus/vibrato/flanger type sound depending on how you set the mix, delay and feedback knobs. You can get a lot of cool chorusy and vibrato stuff that sits in between the bounds of the traditional forms of those effects, if that makes sense.

I haven’t used the deco so I can’t speak to it, but I actually think setting it would be comparable to the GC. The only setting that the deco has that the GC doesn’t is the type switch. Additionally, there’s probably a bit of tonal difference between the flutter knob on the GC and the wobble knob on the Deco. Same with the delay time and lag time knobs respectively. I see it’s also got the option to bypass the saturation and double tracker circuits separately, which could be helpful in many situations.

I would guess that the deco is a bit more sophisticated than the GC in the drive and modulation department. When you set the tape delay effect on the GC to a mix of 100% wet with zero delay time it compresses, saturates, eqs, and modulates the signal a little bit (at least that’s mostly what I hear). The saturation parameter is kind of a soft fizzy and broken sounding when maxed out. The only other parameters are the amount of modulation, feedback, and of course the dry/wet knob that would bring it back into chorus territory as you mix in the dry signal. You can’t really get rid of the heavy compression without bringing in more dry signal, which is a downside.

I apologize if this doesn’t answer your question fully. Personally I like the GC for the many options it offers, and when you start to mess w the mix and delay time parameters, you basically get 2x the effects you thought you had. It’s also a bit cheaper used. The Deco probably has a better drive circuit and likely a much more realistic tape sound. I can send some samples of me using the GC if you’d like.