Array of Objects or Array of arrays?
Keep related data together.


Does your application need a list of contacts? Keep each contact intact with the second approach. Merging data to create and pass a single contact takes work and is error-prone. 
Does it need a list of contact IDs? Do the same or return just that list. With the latter approach you can easily produce a limited array. Going the other way is much harder (more code).
Does it need a list of contact names in a drop-down that loads the full contact for one ID? Use the latter since you get everything up-front. 


The short answer is Keep related data together because it's generally easier to pull it apart than merge it back together.