I think it's worth noting that Cold has 3 powers that are purely ally buffs, and thus of almost no use while soloing. 2 of those, the defensive ice shields, are really good team buffs of the fire-and-forget type, though.
There have been other postings about the value of Radiation Emission vs. Cold for defenders as well as corruptors. A new discussion of how the water blast powers augment and synergize with rad or cold would be better dissected.
Because of water burst and the AoE knockdown, in my humble opinion, water burst helps rad to keep the foes bunched up for the toggle debuffs. With snow storm and sleet, cold users already have the slow and knockdown to keep foes bunched up.
To the OP, Radiation has Lingering Radiation and EM Pulse. They are AoEs and they are stronger -regen attacks than what cold uses. Cold has heat loss for resistance debuffs, and it is AoE and it is a stronger resistance debuff than Radiation's enervating field. Sleet is one of the most powerful debuffs in the game -defense and -resistance. It's AoE as well. As an aside the strongest -regen power is poison gas trap from Traps, and it is an AoE as well.
Triumphant Defenders Forever
Psylenz FF/Psi, ArticQuark Storm/Rad, Symon BarSisyphus Bots/psn, Max VanSydow Thugs/Dk, Cyclone Symon Bots/stm, Blue Loki Ice/Cd, Widow 46526
HelinCarnate:OMG it is so terrible. I have the option to take 3 more powers but no additional slots. Boo F'ing hoo.
Rolling a new defender but I'm stuck on the decision wether to pair the new water blast with rad or cold. Rad gives AM a heal and all of its debuffs are aoes. Cold has arguably stronger debuffs towards hard targets being that they are ST, the debuffs aren't toggles it gives a boost to def via artic fog and I should be able to get by with sleet and waters soft control to deal with spawns quick enough. Asking the advice of the forums in case there is anything I have overlooked, or some angle I'm missing. Looking for all around pve, may try to see how I can push the envelope on bigger game hunting later on. Thanks in advance.