Both Nikon D3400 and Nikon D5300 have 24.0 MP resolution sensors but Nikon D3400's sensor is APS-C (23.5 x 15.6 mm ) and Nikon D5300's sensor is APS-C (23.5 x 15.6 mm ).
Since Nikon D5300's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon D3400.
Another similarity between these two cameras is that both Nikon D5300 and Nikon D3400 sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the D3400 and D5300 sensor size comparison.
Nikon D3400 and Nikon D5300 sensors have exactly the same size so none of them has any advantage over other in this area.