FIFO, LIFO, and Weighted Average Effect

Why does FIFO produce higher net income than LIFO during inflation?

Older, cheaper costs flow to $COGS$, so gross profit is higher.

Under falling prices, how do FIFO and LIFO effects compare with the inflation case?

They reverse.

What is the trade-off between FIFO and LIFO under inflation?

FIFO improves balance sheet realism; LIFO improves income statement realism.