One thing to consider 1st is how much will you let the players know of the Secret War and will you put any restrictions on allowed characters.
If you keep them ignorant and limited to just modern characters
Sleeping Dragon Awake and Baptism By Fire are good intro secret war adventures.
Legacy of Ming is good too if you do some modifications to it, and just turn it it into a treasure hunt against competing forces.
A thread exist of the favorite least favorite official 1st edition adventures that you may want to check out. In which people posted their favorite and least adventure and why.
https://forum.atlas-games.com/t/favorite-least-fvaorite-official-adventure/9470/1
My personal favorite was Shaolin Heartbreak.