Daytrader; you're nearly there.
On a four engine jet, the critical engine is the UPWIND OUTBOARD engine.
a) due to the thrust line being furthest out
b) weathercocking of the aircraft into wind because of the very large tail.
On most two engine jets it will be the upwind engine, although flapsone has come up with an intriguing example of the 125 doing something a bit different.....