I can't speak about the differences between the particular airfields you mention, but I would tend to go with the one with the best instructors.
I did my PPL intensively, spread between PA38s and PA28s and within reason, getting experience on more types isn't a bad thing. I would tend to do initial circuit training on an aircraft with mixture controls and carb heat because getting into the habit of using them correctly is important and this habit would be easier to get into if you start using them from the beginning. That said, I would personally be interested to fly a diesel and it may be reasonable to fly the later stages of your course on one.
Which airfield gets you to the area where you will practice maneuvers such as stalls and pfls the fastest? This is likely to make a significant difference to the price of the course. You may get more practice at crosswind landings if you fly from a controlled airfield with more than one runway. If you have the money to pay for the course outright then consider staying in a B&B and doing the course somewhere cheaper, intensively. You'll also be much more likely to get the PPL in minimum hours that way.