My daughter has around $25,000 to spend and needs a 4x4 diesel twin-cab ute capable of towing a tandem horse float with two horses on board (about 3.0 tonnes). Of the VW Amarok, Mazda BT-50 and Ford Ranger, which would be the best for the task and value for money. I am concerned about the VW's small engine.
The Amarok is rated to tow 3000 kg, which would make it marginal for your needs given that you want to tow around three tonnes. The Ranger and BT-50 are rated at 3500 kg, which would make them more suitable for you. The Ranger and the BT-50 are the same vehicle, it's only the features that separate them. For me, of those you list the Mazda is the best value-for-money.