Of all these I'd choose data: it is defined for the nodes implementing CharacterData interface (Text and Comment ones) only. Trying to access this property for the others gives undefined.
nodeValue is essentially the same as data for text nodes, but is actually defined for attribute and comment nodes as well. And I usually want my programs to fail early. )
textContent is, for me, something completely different, as it represents the text content of a node and its descendants. This, along with wholeText, perhaps should be used more to collect texts from more complex structures than a single text node.
Said all that, textContent and wholeText were defined in DOM Level 3 (= more modern).
