Have both lenses.
Summilux advantages;
1-Sharper at wide open.
2-Contrastier at wide open.
3-Better color reproduction at wide open especially for skin texture.
4-Tele than nokton, nokton is wider.
5-Better (smoother and creamier) bokeh at wide open.
Nokton advantages
1-Differences may not be significant for some users.
2-Much cheaper.