I use a Fire/FF controller and I must say I find him great. I cannot comment for certain on fire/rad but to be honest I would just try playing with your character and see what you think. If you don't like him... re-roll (Ill/kin is fabulous too).
No matter what, have fun
agree with threads - having fun and choosing the powers u like is the impt thing. stop crunching numbers - u'll just hav to play with different strategy! I am a ice/rad. suits me fine! 
Thx got troller up2 lvl16 nw. Gotta say FIRE rules!!! 
"We're not tools of the Government or anyone else...
Fighting was the only thing, the only thing I was good at...
But atleast...I always fought for what I believed in!" (Gray Fox)
@Captain Paragon EU @Captain Paragon.
as a level 50 fire controller i can say that fire is awesome, in pve i can easily go from group to group beating enemies with ease, in pvp i can hold my own as well, dont listen to any of these "uber" builds, just do what u enjoy
w00t fire ftw! i have a fire controller and im determined to get him to 50 before i even think about CoV thats how much i love him besides it has the coolest pets i've ever seen :P and they do insane damage
Seen Daybringer? She's a fire/storm but the sheer amount of damage she deals puts her on the Damage Dealers boards (on the weird rotatey information thing) nearly every month, up amongst the fire tanks, scrappers and blasters.
The Imps are squishy so bubbles are quite good on em. As for the Fire/Rad thing, well my troller is Fire/Rad and is pretty tasty, however the extra damage you give the Imps with AM and EF isn't as great as you might think. At least with FF secondary you could just get the buffs saving you a lot of power and enh slots.
For sheer damage Fire/Kinetics is the best build, I saw my Imps smacking some mobs after they had been Fulcrum'd....simply amazing. Rad is better than Kin from a defensive/control viewpoint however.
I have recently made a fire/ff troller an i have been reading the board due to updater patch
and alot of people have said that fire/rad is the best choice?? I chose ff as secondry because i though that ff has some dam resis as well as hold resis etc. So fire which does most dam out of troller primary+ FF which has some defense will be great combo am i wrong 
"We're not tools of the Government or anyone else...
Fighting was the only thing, the only thing I was good at...
But atleast...I always fought for what I believed in!" (Gray Fox)
@Captain Paragon EU @Captain Paragon.