Vmc is calculated using a 5° bank into the dead engine, thus reducing rudder required. If you now fly straight and level, you'll need more rudder and will be slipping through the air reducing performance on what could already be a dangerously under-performing aircraft. If you're at Vmc with a 5° bank and you now level the wings, you'll be below Vmc [or Vmc raises] and loose control, or at least you won't have enough rudder authority to remain in control with full power on the good engine.
For a fairly simplistic view....
Bank into the dead engine and you increase your chances of not coming out alive. Vmc will be higher as you have more forces to overcome with the rudder [weight of the dead engine for starters].
Bank into the live engine and you're chances are better, before the aircraft can loose control it has to overcome the forces keeping the live engine down for example.
I for one would not bank into the dead engine especially at low airspeed and trying to maintain altitude or climb unless there was no other option. You can be pretty sure that most ME fatalities during an EFATO are the result of the aircraft speed dropping below Vmc and the aircraft loosing control, so no point in exacerbating your problems by turning the wrong way.
I would be very dubious about attempting a go-around in a Seneca [any of them] on a single engine. The POH states that this is "Not recommended" anyway.
Rgds
EA
