it really is a personal choice- when i did mine for my brother i stuffed them fairly (full) but not firm- but his is a denim quilt---
he brought me a whole garbage bag full of denim pockets-removed from his work aprons- and wanted me to make him a quilt with them- i stuffed the pockets then sewed them together- they were like little throw pillows- squishy-but full.
I would think it depends on the look you want- and who it is for- some people may like them flatter than others.