Option A sounds the coolest. Some things that I'd be interested in:
1. bring Benjamin Franklin to today's time and have him ride transportation, see modern technology, etc and then see what he does when I ship him back to his own time
2. Have a "swim party mishap" with Charles Darwin to see what the world would look like without Origin of the Species
3. Change pivotal history moments that affect today (e.g. warn Abraham Lincoln of assassination, warn about 9/11 beforehand, etc)
For Option B, I'd want to visit the 1950s.