Nexus 7 2013 hands down in comparison to Galaxy Tab 8 (GT3).
GT3 have low resolution on large screen which comes to a PPI of 189. Whereas N7 2013 have a PPI of 323 (comparable to Retina display of iPhone 5).
Apart from that N7 have more RAM, better video camera (1080p), scratch resistant Gorilla Glass, better CPU and GPU.
Only better thing in GT3 is bigger screen (but less PPI) and more mAh of battery (but then Mali 400 MP GPU of GT3 consumes more power than the Adreno 320 GPU of N7). [Ref: *pchelpinfo.com/which-gpu-is-better-mali-or-adreno.html]
Also GT3 have a physical button, which can be an annoyance if you use your tab in landscape mode. But N7 have no physical button so it takes a little screen space of 7" screen. So choice in this regard is subjective. (I prefer no hardware button, since those gets damaged quickly).
Also N7 is pure Android and developer support is unmatched. You can install Ubuntu Touch on N7 later when its becomes more stable.
