I have cooked on a number of SPK500's and own one as well. I have NOT personally cooked on an OH, but have a number of friends who have, and I have tasted the product. I thought i'd throw in my 0.02, fwiw
I think both smokers are excellent, turn out good product and are very easy to use. Basically, as the cookers go, there are some design differences, but looking at the big picture, they are pretty much the same. Buying new, OH has an edge on price in comparison to the SP, but the SP's are much more widely used, and have a better availability of parts. I can't speak to OH's customer support, but SP's is top notch. I own a 22 year old SP and they still support me as if I just bought a new one from them. If you are depending on the unit for your business, you need quality support.
Good luck!