I can't really talk about Icy Assault, since I haven't used it yet, but I'm strongly considering an Elec/Ice dom as one of my GR characters. Icy has decent AOE capability between Ice Sword Circle and Frost Breath, which is important to me, and the ST is not bad either, so it'll still contribute well vs. AVs. I suspect I'd probably just skip the melee attacks entirely, as the blast attacks ought to give a sufficient ST chain for most situations.
I do have an earth/thorns that I've gotten up to 37, and I have kind of mixed feelings about thorns. The good side is three powers with AOE, but on the other hand there are a few long animations (especially Thorn Burst) that can be frustrating at times. Still, Ripper and Fling Thorns are really great cone attacks (the arc on Fling Thorns never ceases to amaze me). I'm looking forward to getting Thorn Barrage to finish off my ST chain.
Both are pretty good assault sets. My own /Ice Dom stopped mid twenties but teamed with them alot and once they get stamina and have the powers slotted, Ice Sword Circle alone is quite impressive.
Thorns for me is a tad bit more rounded as the single target attacks at range and in melee are solid and the cone is good too (and early but a little less intensive than ISC). Thorn Burst is a bit weak, particulary if you don't have a power like Artic Air to help you out when jumping into the middle of a mob. I never really took to its tier 9 power (does do knockback which might mesh well with Elec) but Ripper makes up for it at 35. Trops is also a useful tool to have and a handy way to save slots elsewhere.
More familiar with Thorns but as I said, both sets are good but I'd take Thorns, fairly safe you'll be more uncommon than the (likely) many rolling Elec/Elec on day one.
I'm going with Elec/Elec sadly - not tried Elec Assault yet 
5 possible pets helping me out seems like fun 
I'm looking for some opinions here. After hearing some info on Electric Control (Gremlin pets YEAH!) I'm all set to roll a new dominator for GR. Granted this is rather premature since we don't know anything about the new primary yet, but I can't decide between Icy and Thorny Assault for the secondary, both look very interesting. For some context, I've already taken an Earth/Earth to 50, and none of the other sets jump out at me. So the giant question mark that is Electric Control aside, what does everyone think of these two assault sets on their own merits?