I haven't done the 6 inch ones but I did do the 10" that is my avatar. Much to my surprise she was fairly easy to paint! I made her more doll like than baby like because she is a gift for my 13 year old niece. So it might have been harder had I tried to make her more like a baby...
I think it's both. Harder cause they're smaller but easier as with the minis you only have to do the 3 colors (if that's what you want). It's sure a site quicker!