Hi, Maggie,
Looks like Mother was right -- I'm a stranger in a strange land!
Here's my reasoning, considering that I don't believe any of these have a significant impact on FAA search placement, or sales:
1. Features are chosen by a single person (moderator) in a specific Group.
Favorites are usually bestowed by many individuals, whether or not they're Group members.
2. Feature badges eventually fall off the chosen artist's product page, so may have only a brief impact on viewers. (Assuming the Featured artist belongs to more than three groups.)
Favorites are saved for viewers (fans!) to peruse, at their leisure and from their own portfolio page, time and time again. A personally curated Gallery of Wonder! (At least, that's how I use my Favorites.)
3. Featured art falls off the Group Overview page, into certain Group oblivion.
Favorites, on the other hand . . . see #2, above. ;-)
If Features led in any direct way to sales . . . well, I'd be typing this from my vacation home on the Riviera! ;-)