I have a Sonic/Kin Corr and he's plain lovely. Siren Song is really all that for a solo Kin. Sleep the group, pick a guy to Stun and ST to death in a few hits. Rinse, repeat.
Rad'd -Def will obviously help in the lower levels, but as your build matures (and especially if you pick up Tactics) it becomes a non-issue really. Of course Rad has a tad more useful AOE.
Sonic, by a [censored] length.
"If you're going through hell, keep going."
Winston Churchill
Winston Churchill
I'd say sonic blast as well. +dam coupled with -res is a truly beautiful thing, and, by the time you hit 22 and get SOs, you should already be dancing with the tohit cap.
Sonic blast for siren's song synergy, and the -res that allows for damage boosting beyond the damage cap.
Definitely Sonic.
Kin/Rad is a nice combo because the Kinetics powers need to hit and rad provides -Def, but its very short on damage mitigation.
Kin/Ice 
Bye, everybody!
*Champion*
"Kin/Ice"
Sssshhh....great you woke the monkey..time to buy more charcter slots..(sigh)
"...well I have wrestled with reality for thirty-five years, Doctor and I am happy to state I finally won out over it." Elwood P Dowd (from the movie Harvey)
Always looking to feed the altitis monkey on my shoulder I have been playing with different kinetic builds..and have come down to two..radiation and sonic. Both have their good and bad sides radiation lots of aoes their defense debuffs help out the primary (ie you laser paint the target and then fire off your primary). Sonic lots of surviabilty and more damage and stacking the damage resitance with kinetic's buffs. So what is your all's opinion on this?
"...well I have wrestled with reality for thirty-five years, Doctor and I am happy to state I finally won out over it." Elwood P Dowd (from the movie Harvey)