I can't speak for the shred stack since I haven't used it yet, but Need2slin and N2burn are a great combination for fat loss, energy, endurance, and minimizing fat gain from eating high Carb meals.
I would say your choice should depend on your diet. If you like carbs every once in a while (like me), do the Need2slin/N2burn combo. If you do a low Carb or Keto diet, go for the shred stack