We have no information to go on. They are both computers, in order to give relative help, we need to have some basics.
Such as
1) what do you use it for
2) why did you choose the MBA in the first place
3) is it not performing the tasks you bought it for?
4) why are you attracted to the iMac?
the iMac is hard to fit in a backpack... 🙂
I cannot imagine being confined to a desk in just one location.