Oh and I owned a OB-12 many years ago (somewhere around 2001 when they were cheap!) I paid $550 for it and later noticed it smelled like a cat peed on it. I currently own a Sledge. Had it about 2 weeks, looks a bit like pee but does not smell like it.
Everything on the OB-12 had the zipper effect. The pitch wheel, glide/portamento, sliders, etc. It had a wimpy and lifeless sound. The effects were useless. What I liked about it was the flexibility and the display. But neither of those things can compensate for weak sound and cat pee smell. So I sold it.
But to be fair I'm contemplating swapping my Sledge out for a Nord A1. The Sledge sounds outstanding, but some of the controls are unpredictable. For example the LFO depth seems to do nothing at lower levels. At high levels, if the LFO cycle exceeds the parameter's min or max value, the sound is truncated during that portion of the sweep. Which effectively narrows the range of the LFO quite a bit. You have to be kind of reserved with it. Then of course there's the fact that the LFO's can't sync between voices, which at some settings can produce very undesirable sounds. (But can also be quite cool sometimes!)
But if you can get past some of these oddities (early Nords had LFOs that behaved much the same) you are rewarded with a very instantly gratifying synth capable of some really huge and interesting sounds. You could go for the much more flexible Waldorf Blofeld but personally having owned both I think that not only does the Sledge sound have more power in my opinion, but you're also more likely to go exploring with those big ol' knobs staring you in the face.
So in conclusion between the OB-12 and Sledge:
- Sledge KILLS the OB-12 on sound. Absolutely murders it. And it's much more straight forward save for the few controls that don't exactly do what you'd expect. (LFO Depth and Osc 2>3 sync I'm looking at you!)
- OB-12 has the flexibility and tweakability, but it's let down severely by poor parameter resolution and a weak CPU.
Winner: Sledge by a country mile.