Any XPath that works today on a particular HTML page H1 may or may not produce the same result when applied (in the future) to a different HTML page H2. If you want it to have the best chance of returning the same result, then you want to minimise its dependencies, and in particular, you want to avoid having dependencies on the properties of H1 that are most likely to change. That, of course, is entirely subjective. It can be said that the longer your path expression is, the more dependencies it has (that is, the greater the number of changes that might cause it to break). But that's not universally true: the expression (//*)[842] is probably the shortest XPath expression to locate a particular element, but it's also highly fragile: it's likely to break if the HTML changes. Expressions using id attributes (such as //p[@id='Introduction'] are often considered reasonably stable, but they break too if the id values change.
The bottom line is that this is entirely subjective. Writing XPath expressions that are resilient to change in the HTML content is an art, not a science. It can only be done by reading the mind of the person who designed the HTML page.
