I presently own both as well as a number of other VAs.
Not sure why so many are digging in the OB12. Do you guys program your own sounds? I have heard them to be buggy but I feel like I might have lucked out. All the OB12s I've owned through the years have operated perfectly (fingers crossed).
When I first got the sledge, I liked it but didn't love it. Now it's grown on me. Especially since firmware 2.1 was released. While I have a whole bunch of VAs and also true analog, I'm now in the process of altering my sledge to fit into a wider, more unique role...because it can.
I'm planning on uploading raw wave data and wavetables into the sledge from the PPG wave mapper, as well as raw sample data from the Fairlight CMI. I think that will offer up a lot of new options that take the Sledge out if the VA realm and into its own.
I'm also seeking someone to help customize a new body for it. I hate that cheap plastic yellow casing! I'd like to build a new wooden casing for it, and maybe change the knobs out for something less chunky. Might also redo the silk screening to lettering that isn't so "Space Robots 2029".
As for the OB12, I always loved it. It's shortcomings are not so apparent for me because I use so many different things I do t rely heavily on a feature set. I will say I rarely write a patch that is more than a double part on the OB12. So, I haven't noticed a lag. I also don't think it's sound structure really needs more than two parts.
I do love the sound of the OB12, but I don't feel like I can really compare the two. As strictly VA instruments, I do feel the Sledge has a sonic advantage, but the OB12 has some beauty in its simplicity. Don't over-program the sounds, but under programming makes the synth sound boring. It has this subtle sweet spot where it shines. Therefore, I don't recommend the OB12 to anyone who doesn't have nearly every other option available.
Also, the sledge is very road friendly. Even if you bust it, another one is readily available on the cheap. My OB12 will never leave my studio.