I consider myself to be a natural or at least naturally-inclined beekeeper (the definition of "natural" varies so much amongst beekeepers that I sometimes hesitate to use the term without context). I personally see sugar as emergency feed only. Is it the best thing for bees to eat? No, certainly not, and your goal is always to leave the bees enough honey so you don't need to feed sugar. But sometimes things don't go as planned. Maybe the fall flow doesn't come in. Maybe a weak colony is robbed out by a stronger one. Maybe you have a package or nuc that is getting a late start and needs a boost. In these situations, if you have extra honey frames squirreled away somewhere, or a big colony with a surplus you can donate to the other colony, that is what you'd do. But if you don't have any extra honey, then sugar is what you can fall back on. It's not the best, but it will keep the colony alive and prevent them from starving to death until they have access to nectar again. Personally, I would be wary of purchasing honey to feed to bees, unless I could get it from a beekeeper who I would trust to have healthy bees. I also feel like the extra expense of a different sugar isn't worth the price for the purpose, since I only use it when something goes wrong, which hopefully is rarely. So I would just use whatever sugar I had on hand in the kitchen.