These two coins seem to do the same thing, make smart contacts easier to use. I think the key difference is the revenue model and th he degree of decentralization.
Blockcat will do better if people need a contract or two occasionally and if the all these icos develop their own contracts and then try to sell the ones they develop.
Ether party will do better if people need lots of contracts and so want a subscription and if the talent pool that can write a contract is so small that it makes sense for many of them to be employed by one organization.
Interestingly, the talent pool argument favors ether party early and blockcat later while the subscription model favors blockcat early and ether party later.
