One is 16 chips to make 4 GB, the other is 8 chips to make 4 GB(double the storage density per IC).
Or wait...you mean the kits themselves? Under the hood, not much difference likely, since only Samsung can really get C9 @ 2400 consistently. Just make sure if you want to use 8 sticks...you buy a full kit of 8 sticks.
And forget about running 2400 @ 100 BCLK with 8 sticks.
Honestly, I don't think you can go wrong here with either kit.. Even if for some reason you ended up with some crazy Hynix MFR under the hood.