Depends on the game, which also reflects the importance of the console to myself. Example:
SNES = Cart Only
N64 = Cart Only
PS1 = CD and Case. Manual if possible but not the biggest concern.
Megadrive = Cart, Manual and Case is always the go to for me.
Neo Geo Pocket = Always Complete, may slightly compromise if most parts are there.
I think that kind of reflects the packaging of the times. SNES and N64 were just crappy cardboard boxes, so they were and always are susceptible to breaking and disintegrating. MegaDrive cases are the thing of beauty.