I like the title of the heir to include the phrase the Crown Prince.
It designates the heir.
The title of Dauphin is nice. However, if you are not familiar with French Royalty, you may not know that Dauphin referred to the French heir.
I think variety is the spice of life - it's nice that different royal families have different ways of doing things, and I suppose the name or title of the heir the throne is one of those things. My preference - at a push I would say a named title like Duke of Brabant or Prince of the Asturias.
I think Crown Prince /Crown Princess of .... In one was it is nice that others have speicial titles like Duke of Brabant, Prince of Wales etc. But on the other hand they are very often referred to as Crown Prince Philippe etc. which they are not.