This is my opinion, if block chain goes mainstream there needs to be a way for everyone to store it. I think if a cryptocurrency had most users store only a small portion of the block chain while legacy nodes ( such as miners and delegates ) on the network keep the full copy, then everyone even those with a cheap smartphone will be able to participate without having to rely on something like an online wallet.

I think this is more important for mainstream adoption than what kind of directed graph is used.

At the end of the day which of these graphs will be used depends on how much speed can be milked from it without sacrificing security.