Genetically it makes no difference which way your start. Planning-wise for future breeding, it does make a difference.

If Spider male/Pastel Female or Pastel Male/Spider female are the only 2 options, I'd go with Spider male/Pastel female.

Reasoning:

Spider male X Pastel females = Bumblebee. Bumblebee male (son)X Pastel female (mom) = Killer Bee

Going the other route, you are stuck on Bumblebee and can't advance past that with those 2 starters (you have to wait until female offspring grow up).

Throwing other genes in there obviously changes things, but if those were my only two options....