I get better flavor from MY compact single coil than I did MY large dual coil attys. But that is heavily dependant on which you are comparing. I have used a lot of duals, and never came across one that puts out the same intensity of flavor as a gr1. But when compared to a pulse 22, a good dual has preformed better.
Airflow (amount and direction), open space inside the atty, coils, coil position, wicking (position, material and density), the composition of the ejuice, and choice of drip tip can all affect the end results. No body can say if one classification of atty is always going to beat another.
With my build, and the atty I chose, I do produce more flavor and vapor out of my single coil than my buddies dual that he runs super low ohm on a 4 battery mod at very high wattage. It always bothers him a whole lot. I think this is partly because of their lack of attention to their builds and wicking. They buy pre made coils and don't pay any mind to efficiency, where I build my own coils specifically to optimize the performance of my atty.
I also have a 30mm dual coil tank that is a fog machine, puts out stupid amounts of vapor and still has good flavor (not as intense as my gr1, but better than some single coil RDAs). So again, it all comes down to design and how well you can build it.
And about best wire type, finding the right wire type, coil position, and coil size for a particular atty is the key. One wire type isn't going to be best for everything, since everything is different and doesn't interact with the coil the same way. Some attys don't supply enough airflow to the coil to properly cool some wire types, but others will. Some attys will supply direct airflow, some indirect, and others will mix the two. All of these will require different build techniques and potentially different wire types to maximize preformance.