Congratulations to you on at least 2 counts!
1- You're doing you homework BEFORE you deal with the sales pitch at the dealership.
2- You are thinking for yourself rather than letting some died in wool Harley or Spyder owner tell you what to think.
As stated many times, these are 2 very different animals. And you add a 3rd variable with the RS/RT choices.
Still, regardless of subjective opinion, there are some inherent characterists due to the laws of physics that are pretty much boilerplate.
2 wheels in front provides a safer, more stable and better handling format than 1 wheel in front. You also get quicker response to steering input (which can feel 'twitchy' to a new rider until they get used to it - then it feels 'responsive').
The angular force exerted in a turn is forward and towards the outside of the turn. 1 centered wheel just cannot compete with 2 spread wheels in resisting this force.
As you can see from my feeble attempt at a visual below, the tipping force from turning is also resisted better with the 2 wheels forward format. If you add braking to your turn the blue line force is multiplied. With the Spyder platform you're getting the greatest stability where it is needed most. Adding aftermarket suspension components to the Spyder can significantly increase these positive traits. There really is little that can be done to the front end of a standard trike platform, assuming that the rake and trail are already correct.
Not only does the Spyder have 2 wheels resisting the biggest force encountered, you get added traction from the 10" (5" x 2) wide contact area
(with the stock Kenda tires). As you can see from the Tri-Glide picture, you may be getting 3" of total contact area.
Of course there is more to a ride than handling and stability. And there are many more differences between these two machines than what I have covered here. Everyone has to decide what is most important to them. Everyone should ride what they like best.