Cadillac_of_the_Sky wrote:
What are the harder aircraft to fly? Who's busier, a single-seat pilot or muti-engined pilot with someone else?

Now that Steve has said there is no answer, I'll give my opinion...(from my VERY limited experience).
The multi engine pilot has more stuff to monitor, and always more to worry about since one engine will always be slightly different than another. Is that becuase there is a problem, or because each engine has its own personality? You don't have this worry in a single engined airplane.
If the engine quits in a single, you land (or jump out given sufficient altitude). Some you walk away from. In a twin, you either keep flying or the second engine will take you to the scene of the crash that much faster- it is just noisier on the way down I suppose. Either way you need to keep the aircraft under control or you are a goner for sure. There are plenty of stall/spin accidents after engine failures either way- trying to stretch the glide too far or turning back to the airport are common errors when under that kind of pressure for singles, and not flying by the correct speeds or mismanaging the engine controls (feathering the wrong engine for example) are common errors for twins.
I think the generally accepted thinking is that a twin is more complicated to fly and takes more training (that is why there is a special multi-engine rating).
In general aviation the statistics show that landing under control is survivable in most terrain, while spins are almost never survivable.
The P-38 and the A-26 are examples of large/heavy single pilot twins. Two pilot aircraft have the advantage I think when the crew is properly trained. With inadequate training you could be worse off I suppose.
So as Steve said, the answer is: there is no answer. There are too many complicating issues. Add the psychological pressure of an emergency to the mix and things get even more problematic.