Chris, there is categorically NOT a "critical" jet engine. The term "critical engine" has a very narrow definition in the aviation world, meaning on a propellor driven aircraft, that engine which, due to the shifting of the thrust line because of the downgoing blade effect (note, nothing to do with slipstream on the rudder, it's all about the downgoing blade producing more thrust than the upgoing one and hence moving the thrust line away from the axis of the engine) will cause the worst assymetry (thrustline furthest from the C of G) if it fails. So it's always the engine which spins down and towards the cockpit, i.e. on an engine that spins clockwise when viewed from the front the LH engine is the critical engine, and vice versa.
There IS a jet engine that will be more dangerous to lose, but to call it a "critical engine" is misleading!