1A argument is likely a loser. People seem to keep forgetting that 1A is a restriction on the government. It has not been extended to private entities who restrict speech. I honestly doubt it will. Their best bet will be the contract action. But, like Fistful said, unless Prager has a bunch of cash, or gets legal representation at no cost (contingency fee agreement), don't know that this will go far. After all, YouTube is a part of Google, and Google could drop a few million on this case without breaking a sweat.