for roleplay specificly I would probably write a background then pick the powers that fit that concept best. The controller primary and secondaries are well balanced so I wouldn't worry too much about the ones you pick.
When I wanted a Aes Sedai type character I created a Grav/Storm because the powers suited the concept, Grav being the 'hardened air' rather than gravity.
I came up with a concept similar to Stargate that the ancient Egyptians gods were actually extra-terrestrial and in my case were actually Rikti. I chose Fire/Rad because I felt that these were the best suited to the nano technology that the Rikti might have used.
Tristar again was based on an idea of 3 jewels of power, light, shadow and dark. Light to heal, dark to destroy and the third to travel in the shadows between. I created an Empathy/Dark defender with stealth and teleport, for concept reasons I would always run stealth when I was porting about.
This is how I usually pick my characters and it works for me. The ones I create without a history rarely make it to double figures.
Tristar
thanks for replying, it's the longest I've had to wait on this busy forum. More to the point, thanks for explaining your technique. Considering I'm interested in the rp aspect of the game I should write a background first. I write a serialised story over at The Metahuman Press, it's about a Brit superhero group called The Militia. Sorry about the advertising but i thought you might be interested.
Doctor Universe, my controller is a grav/rad controller(I made a mistake when i said emp)as i was trying to create a believable power set. Thanks for sharing your ideas though, I'll do the same.
doc
Mind or Earth are considered the strongest control sets for pure control. Mind maybe has the edge but no pets. Earths "Mr Poo" isn't a great pet though.
Fire has strong "hard" control (the mobs can't do anything) but no real soft options like Fears. But Fire does good damage.
Grav does good single target damage and ends up with good control but its comes relatively late with their pet.
Illusion has good damage and the best opener power in the game probably in Phantom Army. The soft control of Spectral Terror is excellent too.
But I tend to end up being concept affected too. Carni was is a demonic imp from some charming hell dimension (her people are primative cave dwellers but not inherently evil. Generally they end up being the ones involved in the truely evil demons experiments, usually terminally). So Illusion / Storm seemed to suit her.
Maloth is alien tech reactivated by Nemises so Fire/Rad seemed to suit the idea that Nemises cobbled him back together with Steampunk tech and his powers are more to do with leaks from his power core and overloads / internal pressures than anything else. So I went Fire / Rad with him
Thanks Carnifax
I like the steampunk idea, it really fits. Mind control appeals but Grav does draw me. 
Doc
For the secondaries I find just holding off a day or two and thinking of the char as you walk home or whatever helps. Empathy is fine but you may find yourself inventing a little past and background for your char and deciding that another secondary suddenly fits which can be really satisfying, even if no-one else even hears about it (I'd never told anyone Maloths history before this thread)
Go grav / rad and have the FotM 1 on 1 PvP build.
50s
controllers: Ill rad , grav rad, fire kin, ice kin
blaster: ice em
scrapper: spines sr
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Grav does draw me.
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So you might say it... pulls you in...? 
Bad puns aside, I would certainly recommend grav/*. It's quite easy to build a concept around (if you want to go that way), and has an extremely good pet in the singularity, which is a tanktroller.
Thanks all
After being advised to change from Defiant to Union in order to get more role play opportunities I'm considering reinventing my controller. He's only lev 8 so it's no big deal and this time I thought I'd see if anyone would be good enough to give me some specific build advice.
I like gravity as my first power as it seems to be the best for control. Agreed?
I have Empathy for my secondary because the healing is useful for me; it's good for teaming, and I'm only reallly interested in the healing to start with so I can really concentrate on my grav powers. What do you think of this way of looking at it? Should I look at a different secondary?
Thanks
Doc
Thanks