I would use favourite meal, not dish. The danger of "dish" is that you could be implying what your favourite type of bowl was instead.

@Belle: ich gebe dir recht, dass "favo(u)rite meal" möglicherweise als alternative Übersetzung eingetragen werden sollte, dann aber für alle deutschen Synonyme. Allerdings hat "favo(u)rite dish" etwa doppelt so viele Rohtreffer in Google ( http://www.google.de/search?hl=de&q=%22favori... ) und die Einträge zumindest auf den ersten Seiten scheinen sich immer auf das Gericht und nie auf das Geschirr zu beziehen.

What is my favorite food? I don't have a favorite food.

alt.

The danger of "dish" is that you could be implying what your favourite type of bowl was instead.
I disagree. "Favorite dish" is a fixed expression and just means the dish (das Gericht) that one likes to eat most of all. It would be very unusual to find it used otherwise. Besides that, a dish, when it doesn't mean Gericht, is not necessarily a bowl. It could also be a plate, a saucer or a glass. If I had a favorite bowl I would say just that: This is my favorite bowl. That's why someone having a "favorite dish", meaning, of all the dishes in the cupboard he/she likes this one best, is pretty weird. How can someone like a plate better than a bowl? That doesn't make much sense. Of course, anything is possible, but this doesn't invalidate the translation. In other words, just because in some highly unusual situation some speaker might use a standard phrase in a non-standard way doesn't mean there is some danger of misunderstanding it in all the other cases.

I would differentiate between favorite food, dish, and meal:
Chicken is my "favorite food", chicken cacciatore is my "favorite dish", and chicken cacciatore with poached spinach, brown rice and red wine to wash it all down is my "favorite meal".
Gibt es auf Deutsch diese Unterschiede?

@5: nicht dass ich wüsste.
Und ausgehend von den Googletreffern für favo(u)rite dish/meal/food scheint mir das auch nicht überall so präzise unterschieden zu werden.