Prime gets you access to a bunch of units & gets you access to upcoming features that aren't available yet. It also nets you most of the units in the game, and access to all of the Airmechs right away.
Starter pack gets you a ton of diamonds.
They both get you VIP silver for life which lets you earn diamonds from the in game quests, plus you should get access to the diamonds in the top right corner.
I'd avoid the starter pack unless you're planning on getting cosmetic items (purple laser beams ftw) and other skins. Prime is the more useful of the two, but the starter pack is a heck of a deal.

I don't think I helped much.
