I had a prophet 6 with similar knobs to what you speak of, and I much prefer the OB-6's knobs. Their larger size allows more granular/smooth turning and they also abstract the feeling of the pots away from the user. The prophets I had (inc rev2) felt a little gritty and less inspiring to use, esp while tweaking live while playing...
If it's just the looks that bother you, I'd be wary of swapping them. They feel great to me.