Percival is rather too snobbish, and
Percy not really snobbish enough, if that makes sense.
I had a distant uncle
Percival who was known as
Percy; he died when I was a baby and I know nothing about him except his name. There have also been two South African international sportsmen called
Percy:
Percy Mansell played cricket in the 1950s and
Percy Montgomery played rugby in the 1990s and 2000s. But because of them I'm more used to
Percy, I think, and for that reason I prefer it though I wouldn't use it myself.
Pierce doesn't sound very close to
Percy; I dislike it as a lnfn, and for its meaning as a dictionary word. I do like
Piers, though - same sound, but with a terminal -z instead of an -s. Since I named my son
Peter, I couldn't exactly use
Piers IRL.