All our single-button cuffs are 70 mm long, while double-button cuffs are 80 mm long, and French and Neapolitan cuffs are 75 mm in length.
The type of cuff that you choose is first and foremost a question of taste. French cuffs are particularly elegant and quite formal. Buttoned cuffs are stand out less, and are probably more practical if you wear your shirt with a sweater.
A halfway house between the two is a Neapolitan cuff, which is an interesting option, particularly if you opt for a different, contrasting fabric for the cuff as compared with the rest of the shirt and bringing the style of the cuff to the forefront.
Finally, the difference between angled, squared or rounded cuff edges is subtle. Nevertheless, we tend to suggest that rounded cuffs are more traditional, angled cuffs are modern, while squared edges look stylish but wear out more quickly and obviously furl more easily.