iPad Mini w/ retina display and / vs. iPad air ?

Hi! I have two quick questions about these tablets.. First of all, I know that if you compare the iPhone to the iPad, the Apps are designed differently. My question is, with the iPad mini w/ Retina Display, are they just using the iPad Apps down-sized or are they using the look and functionality of the iPhone apps sized up? Also, which tablet do you prefer and why? Just wondering. Thanks. :)