Swift diesel for drivability and mileage. i20 diesel for space, comfort and slightly more power.
Also, the i20 gives you a premium feel over the Swift combined with the option of an autobox, if you need it.
you won’t go wrong buying either of them. The new i20 will likely be launched in the next couple of months. Have a look at this story : http://www.cartoq.com/hyundai-fluidic-i20-launch-seems-imminent/