Sngs are a lot easier to learn therefore I recommend starting people out there. There is the trouble though making the transition from sngs to cash as was brought up, however any solid player should be able to make it. Sngs teach a very important part of poker, which is mainly focused on preflop. Once you learn how to play before the flop, switching to ring expands how you think and you learn to read/put people on hands.

I just think it's easier to give my friend $100, show them how to load a tournament, and teach them to fold fold fold pound pound fold fold push push, rather than to flop sets and spot big hands.