Having instructed, flown single pilot air taxi/freight and now multi-crew bizjet I can honestly say that they all have their up and downsides.
However, the air taxi time was by far the most demanding flying that I have ever undertaken. Only those that have flown for 4 hours across Europe at FL90 at night in bad weather at -15 whilst trying to programme a 20 year old KNS80 Rnav box and read a torn low altitude enroute chart will know what I mean. It defines loneliness, especially when the only company you have is a liver in an ice box! It taught me more about myself than any psyco. test has ever done.
Would I go back to it from my comfy, heated cabin at FL400? Probably not as the total job is still much the same. I just do it higher and faster now and share the workload with another pilot (who, like most of my colleagues flew single crew commercial in a previous life).