Char siu (Chinese: pinyin: chāshāo; Cantonese Yale: chāsīu) is a Cantonese style of barbecued pork.
Your options are:
Pork loin;
Pork belly, juicier and fattier;
Pork butt (shoulder), leaner;
Pork neck end, well marbled (jyu geng yuk).
My personal preference is either the shoulder or the neck end for that juiciness without too much fat or being dry and overcooked.
The first thing to note here is not the preparation time or the cooking time, but the marination duration of up to 2 days!
Download the .pdf from this link: Char_Siu_Pork