Changes

A rule of thumb concerning eggs is that eggs with a longer distance typically give you rare pokemon. Although the list isn’t 100% correct (I got a [[Magicarp]] out of a 2km and a 5km egg), see this list at Serebii to check which eggs have been documented to spawn which pokemon

I would recommend using the long distance eggs, 10km preferably or else 5km if you don’t have 10km, in the incubator that has limited use. This way you get the most out of the "breakable [[incubator]]".

This is the currently known rewards list for leveling up.