I believe we need a little more to go on than that. You dont usually ask a tech question on the discussion forum. What track? What type of car? What class? What association? These will help in determining your answer. more information may be needed though.
Well after a quick look of the rules your stuck with stock appearing clutch or tourqe converter, so if running a G.M. a 3 speed or a powerglide will work for ya, I think I'd prefer a race preped powerglide