You don't get to choose.

The notches in the bridge saddle and the nut are sized for the strings. Remove the octave strings, the thinner ones. The B and high E pairs are identical, but you should keep the spacing consistent by removing the same string from each pair.

You will end up with an offset in the strings toward one side of the neck, but that's as good as it gets without replacing both the bridge and the nut with parts that are tailored for 6-string use.