Alright, now that I have decided my villain, I need help with my hero. But don't worry, I already have AT/primary picked, just need help with secondary (because we all know secondaries make or break the hero)

So, I've decided I want to be an Illusion controller, but don't know which secondary to side with. I know that radiation is good, but I would have trouble picking powers.

Controller secondaries are all buff or debuff. To answer that, consider where your damage comes form.

Illusion gets its damage from 4 sources:
1. Yourself (Spectral Wounds) - Mostly unbuffable
2. Phantom Army - Completely unbuffable
3. Phantasm - Buffable
4. Deceived enemies - Completely unbuffable

I would stay away from buff sets (Empathy, Thermal, Kinetics, Force Fields, and maybe Sonic). The problem would be that your buffs don't go where you want them. For example, PA are a nice damage-dealing power. But they can't benefit from Fulcrum Shift or Speed Boost if you go Kin.

(Which is not to say they'd be horrible, just that it doesn't seem like the perfect fit to me.)

Therefore, I would go with a debuff set: Trick Arrows, Radiation, Storm, maybe Sonic.

Sonic we'll toss out because one of the best debuffs, Disruption Field, requires toggling around a melee ally. And PA would fit the bill, but I'm pretty sure you can't disruption field the PA (it's treated as a buff that debuffs. Go figure.) And Phantasm is ranged.

So we have 3 choices:

Illusion / Trick Arrows
Benefits:
* Trick Arrows are loved by some teams, especially quality players, but are undervalued on the whole. So you'll be less common but not unappreciated.
* Illusion uses a "placed effect" in Spectral Terror, so it want's the enemy pack in one place. That combos well with Glue arrow, Poison Gas, Disruption, Oil Slick, and EMP Arrow.
* Glue arrow and Oil Slick keep group together to make up for lack of mass immob.
* PA opening fights will give you time to get lots of debuffs down, which will help in longer battles.
* Ice Arrow stacks with Blind and Flash to quickly hold bosses
* Your pets don't really need a heal. (PA are invulnerable, Phantasm doesn't take much aggro). And you can get Aid Self if you want.

Drawbacks:
* You have no way to light Oil Slick (Unless you go tech and use your inherent power for your whole life.)
* No mez protection.
* Only slight to-hit debuffs, so attacks at you will probably hit. (And mez)
* No -regen debuff (which is a glaring fault of the set itself).

Illusion/Radiaton
* Everybody always loves to see Radiation.
* Accelerate Metabolism buffs yourself
* Choking Cloud is PbAoE mag 1 hold, stacking with Flash PbAoE mag 2 hold to get multiple bosses (at close range). Alternately EM Pulse is mag 2 with crits, stacking or alternating with Flash
* Lingering Radiation keeps group together to make up for lack of immob
* Mez resistance in AM, though not protection

Drawbacks:
* Everyone has Radiation. It won't seem that special.
* Radiant Aura isn't that good of a heal. It's fine for touching up yourself, but on teams the expectation may overreach the effect.
* Debuffs via toggles. If anchored enemy dies, debuffs disappear.
* Debuffs via toggles. If you get mezzed, they have to recharge and reapply.
* PA can't benefit from your AM buff.
* Very draining on Endurance, at least until stamina + slotted AM + set bonuses

Illusion/Storm
Benefits:
* Potentially powerful PvP build
* Snow Storm, Freezing Rain, or skilled use of Hurricane & Gale can keep a group in position to make up for lack of immob.
* Has potential to go "functional chaos", not caring about immob. (Or phantasm knockback)
* Extra summon-type pets Lightning Storm & Tornado for battlefield confusion
* Stacked Freezing Rain is higher resistance debuff than the other two sets

Drawbacks:
* Storm is good in corners, but in open space really wants a control set with -kb protection. Tornado is nearly impossible to use w/o immob or a confined space.
* Thunder Clap doesn't stack with anything
* o2 boost doesn't heal you, which is what you need.
* No mez protection
* Defense via toggles. If you get mezzed, they have to recharge and reapply.
* No -regen debuff
* Steep learning curve.

So there are plusses and minuses for each. I personally have an Illusion/Storm, been 50 for about 3 years now. Were I to do it over again I think I might have gone Illuson/TA instead (and made my Grav/TA a Grav/Storm perhaps), but TA didn't exist at the time.

(p.s. I also have a Bots/Traps MM so I think you made a good choice there already)