Method for setting 6' wood fence posts in clay soil
It doesn't much matter.  The Simpson post base listed by @Dotes will work fine, but it's probably more expensive than just digging a hole and filling it with concrete.  

Something like a Metpost just banged into the ground will probably be easiest to put up, but it is very hard to get the posts exactly vertical (by the time you have fitted the post, it is too late to adjust the angle of the spike).

A wooden post set in concrete will eventually rot, but it would last 20 years in the UK, and Ohio looks like it gets colder in the winter and dryer in the summer than the UK. I wouldn't worry about it.