I've stayed at both. Both were lovely in their own way.

One thing I noticed is that at the St. Regis the staff (at least restaurants/front office) is mostly brought over from France while the Four Season has hired more local people.

I enjoyed the more Polynesian atmosphere of the staff at the Four Seasons and their warm friendliness.

One of the very attractive staff members at the St. Regis told me all the kids (in their 20's) come over from Paris on contracts thinking it will be cool to work in paradise.

They get there and realize there is absolutely nothing to do when they do have time off and get bored to tears really quickly.

I'm not sure this is true, but it was explained to me like this.

For some reason paying $12 for ice tea is a bit easier when it is served with a warm style and no attitude.