Illusion works better with a debuff set due to the nature of phantom army. I personally would go /Rad or /Trick Arrow
Illusion also benefits from any self-buff to Recharge, which means Kinetics or Radiation.
Radiation really is the best choice numerically. I enjoyed Illusion/Storm a lot though.
You've got a good set of anti-AV skills there, with Tornado doing the damage blender on top of Freezing Rain while the Phantom Army tanks for you.
Anything works really depending on what you're trying to get done. You're likely to hear a lot of votes for Illusion/Radiation, which is a really good combo, but IMO other combos are very good too and somewhat underrated. Not being able to buff your army pets may or may not be an issue depending on whether you do a lot of stuff solo. Recent tweaks to the game have made it so that just about any combo can get perma-Army now, and laying your hands on Luck of the Gambler +recharge IOs is much more doable thanks to morality missions.
Speaking about solo performance, Illusion/Rad and Illusion/Cold tend to be among the top performers, with Illusion/Storm well up there. Illusion/Kin is perennially popular. If you're going to pay for IOs, its my experience Cold benefits much more than Radiation or Kinetics although none is really "the best." Trick Arrow also makes up for several of the holes in Illusion and benefits rather dramatically from the +Recharge necessary to keep Phantom Army active.
The "buffier" sets like Empathy, Force Field, Thermal, etc are also not bad choices. Your army won't benefit but your team will. This game's powers powers developer, Castle, has said that he plays an Illusion/Empathy Controller and finds the combo very powerful. Your mileage may vary depending on what you expect to get out of the combo.
There is no question that Illusion's most popular pairing is with Radiation, and for good reason. Radiation is the only secondary that provides a Recharge buff (in Accelerate Metabolism) and strong debuffs that can make Phantom Army better. Phantom Army (PA) is the most important power in the set, and Radiation makes them better. PA cannot be buffed, so the only way to improve their Damage and Accuracy are through Resistance and Defense Debuffs. Ill/Rad is one of the strongest sets in the game, even if you don't try to get Perma-PA. Illusion is single target focused, so don't expect a farmer.
Kinetics has a Recharge buff, but no debuffs. Trick Arrow, Storm, Cold, Therm, Sonic all have some kind of debuff, but no Recharge buff. Empathy and Force Field don't have either a Recharge buff or any debuffs. Not to say that the other secondaries aren't great, as Illusion works great with ANY secondary. Similarly, Radiation works great with ANY primary. But the two of them together have a synergy that no other pairing has.
After Rad, my personal favorites are Storm and Trick Arrow -- I've taken all three of those to 50. Both of those combos have extra damage from the secondary. Cold has extra single target debuffs that may help it be stronger against tough single targets like AVs -- I'm tempted to try that combo. Ill/Kin has great team buffs, but it also has some synergy problems -- especially with Phantasm, since he likes to knock anything in close range of you back. Ill/Emp is a great team healer/buffer, able to distract foes to get in there to be a field medic, if that's what you want to do. Ill/Therm also has those benefits, but can also debuff.
Take a look at my Ill/Rad guide even if you choose a different secondary -- click the link in my sig. It has a lot of help with slotting and strategy for Illusion. And if you go with Ill/Rad, the guide will have a ton of information for you.
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Guide Links: Earth/Rad Guide, Illusion/Rad Guide, Electric Control
Wow, thanks for the advice guys, this really helped in my chosing what to make.
I had always like the way Rad worked, just never got one high enough level to have fun with it. I had also forgot that you couldn't buff the Illusions pets, so that would of been a mess if I had chosen a buffer.
I was more or less looking for a Controller to take on Task Forces, AV Teams, Missions and the sort. I already have 3 toons that can farm so I'm done making farming toons. Sounds like Ill/Rad will be my next project 
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My 50's: Windigo - 2 (Fire/Fire Tank), Rocky Wall (Stone/SS Tank), Obsidian Pain Spike (Spines/Regen Scrapper), Thunder Tower (Elec/Shield Scrapper), Messiahbolical (SS/Fire Brute)
Virtue Current Projects: Isaac Night (32 Ill/Rad Troller), Grim Marauder (30 BS/Elec Brute), Genesis Tide (22 Psi/Time Corr)
Ahh, sounds like you already made up your mind but I'm a bit curious why almost no one mentioned Ill/Sonic. It's a weird hybrid of buffing for team situations and debuffing for both solo and team situations. It has a bit of self-mez protection (which I like, personally), Clarity, and -res debuffs that distinguish it from the Ill/FF option.
Frequent boards reader, once-in-a-blue moon poster.
Ill/Rad is a great choice; it's only weakness is it's lack of AOE. It can tank, it can solo virtually anything in the game including GM's and it's always a benefit to any team.
I have one at 50, perma-PA and it's a real beast. It solos missions faster than my soft capped BS/Shield scrapper thanks to invisibility, PA, Spectral Terror and Deceive. It's a lot of fun to play and very different from a melee character. As long as you don't want it to farm then you won't be disappointed.
COH has just been murdered by NCSoft. http://www.change.org/petitions/ncso...city-of-heroes
So I just IO'd out my first 50 since I started playin again (5 year break), which was my newly made farmer (Elec/SD Scrapper). My problem is I have 4 50's that are all up in your face melee types. I was looking into getting into the field of Controllers minus the ones I do have (Grav/Kin, Elec/Storm (Which are both kinda boring)), and I had always wanted to try out Illusion.
My problem is I don't know what Secondary I should try and what would be needed later on end game. I know Kin is most likely my best bet, but is there any other choice beside Kin? I had a Fire/FF controller up to 41 before the nerf to how many pets you could have out at a time and I deleted him (Having 9 Imps all Bubbled was just to awesome), which I am regretting now. I'm open for anything including Kin along with a build to go by, just looking for good suggestions.
Also this toon will be made on the Virtue server if anyone is up for a leveling team of some sort? This game isn't all that great solo, never has been to me =/.
Thanks in advance!
My 50's: Windigo - 2 (Fire/Fire Tank), Rocky Wall (Stone/SS Tank), Obsidian Pain Spike (Spines/Regen Scrapper), Thunder Tower (Elec/Shield Scrapper), Messiahbolical (SS/Fire Brute)
Virtue Current Projects: Isaac Night (32 Ill/Rad Troller), Grim Marauder (30 BS/Elec Brute), Genesis Tide (22 Psi/Time Corr)