I do both, but don't really go OTT on either.
When our elf arrives, she brings an exciting breakfast (usually doughnuts!), advent calendars, a pair of Christmas PJs each, a letter to Santa kit and a December reward chart.
On Christmas Eve, when she leaves, she leaves behind a bag of goodies to occupy the boys on Christmas Eve. This year they will have a second pair of Christmas PJs, popcorn & Christmas biscuits to eat while watching a film, some Christmas choccies and hot chocolate cone for after bath time, a special Christmas bath treat (usually something like a bath bot from Lush) and a Christmas sticker book to play with through the day. They both get a Christmas themed toy as well. DS2 has a Christmas Happyland set this year and yet to get DS1 anything but thinking a Christmas Playmobil set.