This is a very subjective question but one that I will share my opinion on.
You've learned about pressure treated lumber, softwoods, composites and hardwoods.
You understand the relative cost, appearance, feel, maintenance and life span of each.
From Pressure Treated To Ipe
Pressure treated lumber is the cheapest but requires lots of maintenance.
Ipe has virtually zero maintenance but is very expensive.
The best deck material should satisfy a little of those contradictory desires; last longer, low maintenance but less