I agree with mlesemann.
(Whom I met at the Woods Hole Film Festival. Hi Mara!)
During the last few years, I've attended panels at several film festivals that included directors and programmers for different festivals.
Out of the total of 15 festivals represented at these panels, every single one of them indicated that they prefer DVD's to online screeners. That is not a scientific survey, but it is good enough for me.
Almost all of them also said that submitting early gives you a little bit of an advantage. (It also saves you money!)
Make sure make a GOOD copy on DVD and test every one before you send it to them. Test it on your PC, but also test it on your home DVD player. (Remember, some festivals may end up using the DVD copy you sent as a screener as the exhibition copy.)
Don't have a fancy menu with deleted scenes, etc, on your DVD. Just a Title page with only a PLAY option. Don't have it so your DVD just starts playing your movie as soon as you put it in the player. (Almost every panel member expressed frustration over this.)
Also: Mark every single thing you send to them with your Withoutabox number you received for that festival.
Lastly, have a strategy for your submissions. Look at the festival websites, ask yourself, do the EVER program films like mine? Also understand that if you want to get into, say, 10 festivals, you are probably going to have to submit to 30-50 festivals.