I think you need to try each way and see what works for you. I'm sure it varies by machine, user, etc. Personally, I have better luck with the feed dogs down. I think success is more of finding the right machine speed vs. hand speed. That can also vary by machine. I got it down pat with my Viking Sapphire, but when I got my Juki, I had a learning curve with the machine vs. hands. I found with this one, I have to move my hands faster than with the Viking.
The eyelashes often happen from going around curves too fast. Keep practicing and it will get better.