I’m going, but not from Newcastle.
Mode of travel? Fewer HGVs on the road at the weekend. Bargains on the last day? You might want to choose based on the lecture programme? Perhaps better to make it two days with over 200 miles travelling each way?
I’ve only gone on the same day each time, so comparison of days is not possible for me.
Maybe take 4 coins (one for each day) and flip them, until there is one odd heads or tails, and choose that day ? 
I avoid planning for the last day, just in case something important arises – leaving no second option.