I would prefer it to be single player. Mainly due to the fact that it's a lot easier than having a party. I think a sort of pet system would be best in terms of AI. This means people and animals. If you controlled a dog and it was set on defend it would try to block enemies from getting near you. Attack makes it attack the closest enemy until it is dead. Let's say that there is a move command. You simply choose what spots the dog would run to and confirm. This would be useful for things such as luring monsters or sneaking into places which you aren't allowed to reach...Humans or summons could act just like pets, except some may be able to move objects and such. Who knows...
