I’ve tried a few – all seem to work pretty good:
1. Magic Bullet’s Misfire Vignette
2. Nattress G Vignette (lots of control)
3. Joe’s Filters: Soft Spot (Invert, Subtract mode, drop blur to ‘0’, and play with controls to liking)
4. FCP Soft edges filter
5. FCP Mask Shape + Mask Feather
6. FCP Four-point Garbage matte – LONG RENDERS (play with smooth, choke feather)
That ought to fully disclose my obsession with the perfect vignette.
-s