A mi cama..

Is there a good rule to know when to use Cuál instead of Que, or are they interchangeable?

The usual (but not infallible) rule would be "Use 'que' when you want a definition of whatever follows es/son and use 'cuál' when you are asking for an example/instance of whatever follows. An alternative (for English speakers) would be if you can reasonably replace "what" by "which" in your question, then you should be using 'cuál'.

Para mi es Madrid, España. Porque es una cuidad muy bonita y interesante.

Mi destino de viaje favorito es Virginia y Maine. Tengo que irme a México, España y ninguno país en Sudamérica tarde o temprano.

para mi, las islas Seychelles

Me encanta Oaxaca, Mexico

Ups, I put this question in the wrong section. Is there some way to move this to the travel section?

Punta Cana es la mia.

Para mi es Baja California, Mexico.

Also, if I were to write your title-question myself, I would have made the mistake of writing, "Que es su destino de viaje favorito" - Is there a good rule to know when to use Cuál instead of Que, or are they interchangeable?

Beul nan Uamh, an Island to the west of Scotland (means mouth of the grave-actually cavern but here it means grave).