I had both....Nexus 5 will appear washed out and requires some post processing to bring out the colour, also tends to be a little noisier than the 1020. You also cannot change the ISO on the Nexus 5 (which is a big reason I ditched the N5 in favour of the 1020)
1020 has better depth of field and produces a higher quality image out the box thanks to the Nokia Camera app - Google have a ways to go with their processing algorithms. (well documented)
You also cannot do long exposure with the N5 and its sensor at low light is highly inferior - something I think they could improve upon with allowing adjustment of ISO setting.
By and large the N5 camera was good as a daylight "happy snapper" for Instagram, social media etc but personally I couldn't compare it to the 1020 for photographic ability and image quality.
I'll find some images taken with both and post them up soon.
Sent from my Nokia Lumia 925