I've owned a couple of Gretsches, Two 6120 Setzer models and a Billy-Bo. For me, the main draw for Gretsch is the pickups. They're a bit different than the Guilds I've owned in that they seem to be made with thinner wood and seemed a tad more lively and responsive in my hands than say, an X-170 which was heavier and more robust. It really depends on what you're after. They have very different necks, too.
One of my favorite guitarists is Brian Setzer. Chasing that tone, I've owned a Guild X170T, a Gretsch SSLVO, a Gretsch Setzer Hot Rod, and a Guild SF III with P90s. The Gretsches nailed the tone, look and feel, but dammit, I wanted a Guild. The X-170 looked and sounded great, but with its Fender HB1 pickups, it just couldn't touch the tone. The Guild SFIII with P90s got me where I wanted to be.
Real 6120 Gretsches (not 5120 Electromatics) are expensive, but they're worth it if that's what you're after.
I should point out that the pickup tone thing is very subjective. Yes, the Guild didn't sound exactly like a Gretsch, but the only one that ever noticed that was me. On stage, all people cared about was the music, and the fact that it was orange.
From a build quality standpoint, IMO the Guild won hands down. I got more comments on my X170T that I ever did on any of my Gretsches. The SFIII w/P90s sounds better and still looks great, but the X170T with it's killer flame, bright orange finish, gold hardware and block inlays just seemed to grab people. Hell, it's been my avatar here for years!
Here's the same dufus with the Gretsch:
Back to the pickups, I actually tried putting gold TV Jones in there, and it looked and sounded great. The problem was that the pickup ring holes didn't line up and I didn't want to drill such a nice guitar. Honestly, if this guitar had come with these pickups in the first place, I think it would have been MUCH more successful. Some day I may get another and have the work professionally done.