Higher pixel density
The amazing retinal display of iPad has 264 PPI(pixel per inch), where as the Nexus 10 boasts of 300PPI
Translates into more clarity especially for high resolution pictures and more details in the display.
Thinner and lighter than iPad
Nexus 10 is 8.9mm thick and weighs 603g against iPad's 9.4mm and 652g. Seems like Nexus 10 is more easy to carry around.
High end processor
Latest dual core ARM A15 processor which can easily match up with the latest iPad's performance. Nexus 10 might win the time race with iPad.