I think they are all good choices.
The GP100 will be more "chunky" than the others in typical Ruger fashion - built like a truck. I've never owned a double action Ruger revolver but their reputation for being well built is widely recognized.
Using my Super Blackhawk as a reference, the Blackhawk is also a very well built revolver and would serve well. You don't mention intended use; if protection is among them I might pass on the SA Blackhawk.
I sold off my Taurus revolver (Model 85 38 Special) to fund another purchase. It was a good gun - I ended up selling it to my boss (wouldn't have wanted to sell him a lemon!). He still has it today. My other Taurus is a PT940 which is a favorite; I am pleasantly surprised in just how well this gun shoots. Taurus guns today are not the Taurus guns of 10 years ago. I think a Taurus would serve you well & I have no reservations in recommending them.
A pre-Agreement Smith, IMHO, is the Cadillac. The lines of the Smith are streamlined & attractive, and the trigger pull quality is legendary. When compared to a Ruger GP, the M19 is definetly not as bulky in build. While I do like Taurus, given my choice between the 2 I would probably give a nod to the Smith, assuming the Smith was used & in excellent condition.
With the exception of the SA Blackhawk as a PD gun, any of your choices would be good. My own personal preference would be:
1). Used, excellent condition pre-agreement M19.
2). New Taurus Tracker
3). New Ruger