Duathlon vs Halfmarathon

I've got a bit of dilemma. I have been planning to enter the Bristol halfmarathon on September 15th, as I'd love to go back to my old stomping grounds and do some running, but then today I saw that on the same day the London Duathlon takes place in and around Richmond Park..... Now I'm trying to decide which one to do - try for a personal best on the halfmarathon in Bristol or make my duathlon debut in London?! Decisions decisions.

The stunning Clifton Suspension Bridge

Richmond Park at wintertime