Single Wall CNTs are more difficult to make than Multi Wall and have superior properties see quote from the Sri Lankian patent that I referenced earlier.

"A SWCNT has only a single atomic layer, whereas a MWCNT may contain, for example, from 100 to 1,000 atomic layers. Generally, SWCNTs are preferred over MWCNTs because they have fewer defects and are therefore stronger. Further, SWCNTs tend to be stronger and more flexible than their multi-walled counterparts. Further, SWCNTs are also better electrical conductors and find uses in electrical connectors in micro devices such as integrated circuits or in semiconductor chips used in computers."