There is a point on the mountain road when returning from LT where your round a bend, still fairly high on the mountain and the entire Samana Bay appears in front of you...it is amazing! There are some pretty great views as you enter LT as well, but for me that view on the way back is a mini-highlight of the trip!
That being said, the new highway is beautiful and you have a great view of the ocean almost the entire drive, but the entrance to LT isn't dramatic at all... If you want to try both routes, I would take the new highway to LT and the mountain road back...