* ダスティン (Dasutin): This is a fairly common and straightforward transliteration, using katakana, which is generally used for foreign words. This is probably the closest to the English pronunciation.
* ダストン (Dastōn): This is another possibility, slightly altering the pronunciation to better fit Japanese phonetics.
The choice depends on personal preference and the desired level of accuracy in representing the pronunciation. There's no universally accepted "correct" spelling.