The most common site of GIST is -
Gastrointestinal stromal tumors (GISTs) 

GISTs are the most common mesenchymal neoplasm of gastrointestinal tumor.
GIST represents a distinct group of gastrointestinal tumors that originate from the interstitial cells of cajal which control gastrointestinal peristalsis.
GISTs can occur anywhere in the gastroinstestinal tract; the most common site being the stomach followed by the small intestine.

Stomach → 50-70%
Small intestine → 20-30%
Colon & rectum → 5-15%
Esophagus → <5%
Ileum
Esophagus
Colon
Stomach