Why prefer a Type 73A?
F6 runs with two kinds of trains. Both have an area where dogs are allowed, and in both, people without a dog can end up in those seats too. The difference is how closed off the area is: a small compartment of its own is simply a bit nicer than a corner of a big open saloon.
Type 73A (electric train). The dog seats are a compartment of their own at the end of car 3: seats 155–174 behind a partition, apart from the rest of the car.
Type 5 coaches (locomotive-hauled). The dog seats are the back half of car 2: seats 29–68, in the same open saloon as everyone in seats 1–28, with no partition between.
With the switch on, Best match favours Type 73A trains: another train needs to be clearly cheaper or emptier to rank above one.