I might as well stick my big nose in as well .......... :o)
New skirting properly scribed (as Karl says) would look best. If this is floor slab settlement (probably one of the most common of NHBC insurance claims) .... then the gap will probably vary.
Scribing to follow the floor shape is tricky, but would take your eye away from what, now, must be an eyesore.
Quad can look ok if done well, but filling or re-skirting would be preferable.
If the existing skirting is painted timber then fill and overpaint.
If it's stained, then, difficult unless you fill with something like brown putty. I can never get caulk to take a stain properly.
If it's PVC, then replace with moulded timber.