Hola Jamie
With "me gusta" the definite article is always necessary:
"Me gustan los deportes"
"Me gusta el cine"
"Le gustan los chicos rubios."
With preferir it is optionall if you are talking about something general:
"Si prefieres (los) deportes..."
"Yo prefiero (la) pizza."
If we are more specific about what we prefer then we do need the article:
"Ella prefiere la muñeca pequeña. La muñeca grande es muy fea."
(She prefers the small dolly. The big dolly is very ugly.)
Without the article this would be incorrect:
"Ella prefiere muñeca pequeña."
I hope this helps,
Inma
