Which transaction would get confirmed in an uncongested network? Scenario:

Mallory sends some bitcoin with a $1 fee
Later, Mallory double spends her transaction with a $5 fee
A new block is found

In an uncongested network with an average transaction fee of ~20 cents, which transaction would most likely go through?
On an uncongested network with an average tx fee of ~20 cents. Which transaction would most likely go through?

The transaction which confirms is the one chosen by the miner which finds the next block. There is no way to know which one they may choose. It may be the first one they saw, or it may be the one with the highest fees, or it may depend on some other factor that is relevant to the miner in question. It is simply up to them.