The square D should be chosen.

If the first red car moves to the squares D or A, the second red has got the option to take a slipstream. In case of square A it takes a roll of 9 or 10 for a slipstream, but just 8 or 9 concerning square D. There is a higher probability for the second variant with 9:36 instead of 7:36 for the first one. Because the second red in both cases can move just as far, the D is the better solution.

If the first red car moves to square C, there will be no option for a slipstream because one cannot drive two squares behind C on the same lane.

If the first red car moves to square B, there are two squares on the same lane to drive, but slipstream takes 3 further squares to be done additionally. There are but two further squares left, what excludes sliptstream.