There and back or circular...

Just back from another great post-work run.  6.41 miles at a 9m 59s average pace.   839 calories.
I got changed as soon as I was back from school.  I drove in today as Dan was going out for food with friends from work.  This meant I was back home by 5:15 and that it was light enough for me to run out of town still and somewhere different!  There is a route which runs down into the next village (all street lit) and then alongside the A45 for a mile (not street lit and with a horrific path that has tree roots coming up everywhere!)  I decided a few months back that when it was dark and lots of cars are heading towards you and you are blinded by their lights this route is impossible.  However, tonight it was just dusk and I fancied a change so gave it a go.  I had an easy 6 pencilled into my running diary so planned to head out for three miles, turn around and head back again.
My body felt great from the start.  My mind was still mega busy working through the past week of events and I was finding the run fun and easy.  Heading out my mind was thinking, "You're only going out for three miles before turning back" and it was much easier to focus on than heading out for six miles.
A friend posted in a blog last month that he always prefers out and back routes rather than circular ones (which I have tended to favour) because he always manages to find shortcuts home with the circular routes and not go as far as intended.  At the time I disagreed, thinking that surely it would be much easier to wimp out and not go as far out before turning back on an out and back route.  Psychologically though, tonight, thinking I only had to run three miles helped push me along and helped me play mind games with myself on the way back to not give up!

A there and back route, or circular?  Pros and cons for each.  Which is best?!