The SGX is kind of an odd piece in my rig because I use mainly high-end vintage gear and pedals; I prefer their sound for both live and recording. I'm not going to generalize and say that old stuff is better, because there is a shit-load of old stuff that is crap - plain and simple; but my faves are definitely from a few years back. There's some excellent new stuff, but its usually more expensive than its worth...
I really bought the SGX2000 Express to use as a direct box, and thats really where this unit shines. Its main use for me is putting down solos direct to the board in the studio (Unconventional? Yes. but its really great for that purpose). I usually use it as the last link in my chain of stompbox effects in this situation - bypassing my amp, and mixing in some of the SGX effects as I see fit.
I think all the effects sound good, but you have to tweak. I also wouldn't say that any of them sound so good that I would consider them a favorite. My stompboxes are better in that regard. When it comes right down to it though, this unit is irreplacable in terms of what I use it for; The solos and melody layers I put to tape through this always sound better than when I mic the amp in the studio - and some of the SGX effects, used sparingly, really add to the sound. Generally, I like the sound and versatility of this unit for practicing and laying down tracks to ADATS at home, but I never use this through my amp live or in rehearsal, because used that way, the sound just doesnt cut it. I am content to appreciate it for what it is: The world's greatest Direct Box. As such, it sits in the big rack in my studio at home waiting for me to bring home some bed tracks to layer, or to whip up some song demos. So to sum up - sound quality is exceptional as a Direct-box, but mediocre as a live-rig pre-amp. Also, a lot of the presets are stinky; you have to do your own patches to harness the power within this thing!
It hasn't let me down over the years, but then again it led a pretty sheltered life in my studio rack. Everything is very sturdy - made out of a thick gauge metal and painted beautifully.
I dont intend to gig with it - Thats not its strength.
My only beef was when the memory backup battery finally died after 8 years, I changed it and I lost all my custom patches. I had to restore the factory settings. In retrospect, I probably should have had it powered up when I swapped the battery, but there was no instruction regarding this in my manual. This all happened before I discovered that program on the net someone wrote to interface your computer to the SGX and save patches as files...
If I could go back and do it again, I wouldnt buy this machine brand-new. I paid too much for what I use it for - That might also explain why I sound indifferent about it. It wasnt worth over $1000 to be sure. On the other hand, I have been using it to great effect for quite some time, and havent found anything to do its job better. Its a great machine. So I would buy it again, because for a couple hundred bucks these days, it would be a steal.