It really depends on what you want. Sonic will give more -Resistance to throw around and stack with Freezing Rain. Ice will give you more -Speed and -Recharge to stack with Freezing Rain and Snowstorm.
Since you solo, I would pick Ice Blast. Sonic takes longer to wind up its damage, and its super cool cone sleep power isn't going to work well with the storm primary. Ice, on the other hand, has solid Single Target damage and Ice Storm, which you can stack on top ot Freezing Rain. Freeze Ray also lets you hold minions or lieutenants which are being trouble, and Freeze Breath stacks -Recharge and -Speed again, which might help on TFs to make your powers more effective on big mobs.
Too many alts to list.
Sonic wins in sustained single target damage. Ice wins in area damage, and in burst single target damage.
Played both. The Storm/Sonic is lvl 50 now, and the Storm/Ice was deleted at lvl 16. ymmv.
I'm so undecided on this one. What should I choose? What arguments could you proponents of each give me? I tend to solo and TF mostly, with a little eight man teaming once in a while. Those with exp with these sets please speak up.