Ric,
Before you build I would try paddling both. I always tell people to buy an old rental or rent from a university or other low cost source and paddle for awhile until you decide just what your paddling preferences are. Then you can put the time into a build or money into a purchase of a boat that is suited for what you need. I have singles, I have tandems, even have a triple and they all get used. I prefer singles, my wife will only paddle in a tandem. Tandems are more efficient, balance a stronger paddler with a less aggressive paddler, are usually more stable, and cost less than 2 singles. They are also heavier, harder to car top, don't allow as much freedom, force compromise, more like a Volvo wagon than a sports car and I agree with the safety comments above but that also depends on your skills compared to the water you paddle in. The older I get the more I look forward to paddling with my souse but I am not sure she would say the same. On the other hand I love to leave the house at 5 in the morning and enjoy being on the water well before the sun rises, something my wife would never do.