Well now this is a complicated matter
Favorite of the basics is strawberry (as long as it doesn't have like, chunks of actual strawberry in it lol) Especially at Cold Stone Creamery they have good strawberry.
Favorite kind you can buy at the store is Ben and Jerry's Dublin Mudslide.
Favorite ever is banana ice cream with grahm cracker swirl, resees cups, and brownies from Cold Stone