It depends entirely on your playback medium. If you're sending your footage to the projector from DVD or video tape, use the appropriate Pixel Aspect ratio and resolution for the medium. If you're playing from a computer, you would typically use square pixels.
Stick with the After Effects presets when creating your comps to be sure the settings are correct.
I'll be playing from my macbook. So i'll make my comp NTSC D1 SQUARE PIXEL I guess! Thank you