The smaller of the two, the Core Prime includes a 4.5-inch display with a resolution of 480 x 800. There's a 1.2 GHz quad-core processor, 4G LTE, a 5-megapixel rear-facing camera and a 2-megapixel offering for selfies. It's by no means spectacular as far as features are concerned, but provides a decent enough design, and if you're looking for a taste of Google's Android on a budget, this device might appeal to you.
The Grand Prime, meanwhile, packs a more sizeable display of 5 inches, but with a resolution of 540 x 960, only manages to muster a slightly better (but still sub-par) pixel density of 220 ppi. The processor is the same as the one found within the Core Prime, although you do get an 8- and 5-megapixel camera combo for the back and front respectively. There's no question that the Grand Prime is the better handset, but there's very little in it.
The Grand Prime costs $189.99 on T-Mobile, while the Core Prime will set you back $139.99. Links to both devices can be found at the source.