Ice Blast. Chilblain is useful against AVs and in PvP but as a damage power it's very costly. Ice Blast does a lot more damage at a lesser endurance cost.
I think BoI, Chillblain and Ice Bolt have the same base damage, but Chillblain is DoT which is less useful. It also used over twice as much endurance as Ice Bolt.
Ice blast does more damage than all 3, but it will need to be slotted. Slotted Ice Bolt does more damage than unslotted Ice Blast (except with domination up).
In my level 41 build I don't have Ice blast, I have all the melee attacks and the cone, and all my attacks are slotted including Ice Bolt. I have chillblain but it is unslotted.
I really should do something about this signature.
The Ice blasts, especially Ice Bolt and Ice Blast are a bit of a double-edged sword. Due to quick recharge, really fast animation and good range they're great for building Domination fast. However they're very bad damage for endurance (although not as bad as Chilblain).
I would personally never get rid of my Ice Blast and feel that the AoEs are much more expendable (although Ice Sword Circle is lovely now that the delay after animation has been removed). That's because in competent teams Domination buildup becomes a problem as mobs are wiped out quickly and running after them to hit with a melee attack takes time. So basically, I use BIB and the melee attacks to do serious damage and the two smaller blasts to build Domination with a side effect of some decent damage. 
This is kind of a moot point though. Ice takes long to get an attack chain so getting all the attacks at low level is a good idea. Later on you can respec out of the ones you like less. But using Chilblain as a damage power and spamming it is a surefire way to kill your already ailing endurance. As a control power it's situationally quite nice at the default slotting.
You say Chillblain, I say no, chillblain, no, chillblain, no.
I have taken it for my Ice/Storm controller though, cause a single aplication on a boss wont stop KD, but with all the damage powers a dom has taking one that's counter productive if used on 90% of foes doesn't seem like a good idea to me
"Well, they found my diary today.
They were appropriately appalled
at the discovery of the eight victims
They're now putting it all together.
Women wrapped in silk
with one leg missing
Eight legs, one body, silk,
spider, brilliant!"
Thanks Chaps...
Looks like Chillblain only useful vs AVs. Might still have to get it at level 35+, given how craptacular dominators appear to be vs AVs...
Nah, I use it to bring down flyers sometimes too. Its oky to take if you have a spare power slot but no spare enhancment slots.
I really should do something about this signature.
Hey Ho Folks:
Heres one. Playing my Ice/Ice Dom and need another Single Target Attack.
Ice Blast vs Chillblain?
I despise immobilises due to ice slick, but single target isnt bad (can use it on held target), and it might come in handy vs AVs etc.
Looking at the description, it looks like Chillblain might compare favourably to Ice Blast, in terms of dps / dpe etc. (Since it is a primary not a secondary).
And Ideas?