In Torchlight 2 there are something like 6 pets to choose from. Are these pets any different in ability or is it just an aesthetic difference?
According to this wiki, all pets are equal.
However, different fish produce different properties when fed to your pet.
Yes, as I came across. There will be times when you get gold or items dropping at a location where you or your pet on foot can't go.
A flying pet can easily go to that place Shift + Click to pick that for you.
Also, when you're on stairs, your ground pet will travel up and down stairs to kill monsters. Whereas a flying pet can fly over stairs (on aggressive mode) & clear the location for you.