Hi again,
Sorry if I am repeating a topic but I am new in here.
Also, I think this topic can stay as long as LEGO Technic exists
Including the latest (2019) LEGO Technic sets/models,
which do you think is the “hardest to assemble”, complex/though, etc. You understood me.
For example, in my opinion, still the 1275 part - 42070 - 6*6 40th year edition 2017 Towing Truck is one of the “kings”.
Waiting for your kind and precious thoughts and opinions.
All the best,
Idris