In my many decades of growing squash, seeds planted flat side up will comeup with shorter fatter stems. The seed shell will usually stay under ground.

Seeds planted edge up will push through the soil easier, so will have thinner and taller stems; thus easier to break. The seed shell will often stay attached to the cotyledons and rip them as they enlarge, thus inviting disease in.

I have found that pointed end up is better than pointed end down, but flat side up is best.

pumpkin type seeds germinate through flat end, from which
they grow roots first and grab the soil. The seed leaves in the meantime are growing and expanding.
If the seed was planted such that sharp end was pointing up, the stem will grow straight up , using the seed tip as a spear head.
But if the seed was planted flat end up, the stem will grow in an upside down "U" shape. so when you seed the seed leaves emerging, their tips are pointing down.

I plant them the first way.
But probablly the third way might be better; that is to plant them flat. This way the seed itself will adjust to the condition and will push through the most smart and efficient way, programmed into their genetic makeup.