As a player I probably wore my full studs for most matches in the UK, and my moulded for the occasional one on firmish ground (and my moulded all the time when deployed since most pitches where the navy ships tend to play were sand/hard ground).
Since taking up the whistle (just over a year ago) I think I've worn my full studs two or three times and my moulded pretty much most of the time. I haven't noticed anything different with the achilles, just that it was easier on the soles of the feet, although that may change with the new Asics when they arrive.