As far as making it illegal, I wonder if the blockchain gets to a certain size where it's easy to detect and delete, if that's not already the case. At that point I think the blockchain morphs into something harder to detect--maybe that technology already exists? I think the coin with the best developers will survive--maybe that's Bitcoin, maybe not.
I'm going with the blockchain that has the most transactions is the most valuable because of the meta data you can glean from it. That's currently Bitcoin.
