I would say both are very effective for current pvp.
Rad having the positive of being able to debuff without worry about missing who you target due the debuffs being toggles. Plus having a nice buff and healing ability helps.
Cold having the advantage of not having to stay in range of the person you hit with the debuff due to most of the debuffs being click powers.
I have both a rad/rad fender and a cold/sonic and cold/psi, both are good for pvp.
Basically both sets are debuff machines, the one sole difference of the 2 sets is that cold does not debuff to-hit like rad does, but cold does have a special effect debuff in benumb that rad does not have either. The slow effects of both sets in current pvp is a complete joke(cold used to slow people to oblivion and back)....just my 2 cents
I'm looking to make a Defender for PvP for a mix of zones (including teaming in them sometimes) and 1v1, and have decided to take sonic blast on them because the set simply has everything I could ask for in it as a Defender. For primaries I'm torn between Rad or Cold.
Rad has AM which gives a little bit of everything plus mez protection which is especially nice. It can also heal itself which is a nice bonus. It has some nice debuffs as well, but two of them are toggles which can be dropped when you get mezzed. On the other hand this means that they have low recharges so if I have a few fights close together or there is a multi-person fight going on they will be available for the next victim.
Cold doesn't rely on toggles for the most part, but it doesn't have a heal either, or any mez protection. It does have a bit of stealth and some resistances, and the debuffs are really sick. It seems to be more recommended than Rad overall for PvP nowadays from what I've seen in other threads.