The reason they went with 24fps when talkies came out was that was the minimum frame rate that test audienced felt worked with sound. Otherwise it was too flickery/jerky. 18 fps @ 24fps is going to appear more juttery than 24fps @ 24fps.
All major pictures of course now use 24fps, and to achieve slow mo is the same way that you are talking about, but they use 48fps, and 72fps (2x, 3x slowmo) or whatever is desired.
"If i'm thinking of editing digitally (say on an avid at 29.97/ntsc), what would be the best frame rate to shoot at?"
Theres very little information here to go by. Please post a new thread in the appropriate forum with as much info as possible (what format are you acquiring, what format will you output to? What is your ultimate destination for your film? What is the subject matter? Are you talking telecine and editing on your own comp, or in a post house?"
i'm looking at a normal speed with no effects.
appreciate the advice."