I've recently got my Illusion/Sonic troller to 50 and I loved every second of playing him! Although the screaming sounds do become slightly like a recurring nightmare 
I think /Sonic trollers are less common because there is a lack of knowledge about what the set does/how it works. When talking in terms of synergy it goes brilliantly with Illusion because you can plant Disruption Field on your Phantom Army and you have your own set of tanks plus a yummy -res debuf 
Also, if your interested in concepts then the whole sound and light manipulation between the two sets compliments one another well.
A lot of the Sonic powers require you to have a targetted ally so in many cases your going to need a pet or a team mate alongside you! This however, does make your an intergral part of any team providing a good boost in +resistance. Similaly, if Sonic is paired up with a more offensive primary you could easily slot into PvP play... sets that you might want to pair it with could be Mind, Gravity or Fire if you wish to be more offensive.
Either way it all depends on personal preference and concept designs but I would recommend either Illusion/Sonic, Gravity/Sonic or Earth/Sonic!
Hope that helps a bit 
I have a grav/sonic and although he is fun in teams, he was really hard to solo. I levelled him to 50 before the changes to the sonic gfx, so back then not only did most people not know what sonics did, but they couldn't even see the effects visually (and Disruption Field used to aggro back to you 
). Although he's a great toon to play in large teams and on things like the STF, I don't think Grav is the best primary to pair with Sonic. Your Sing doesn't really need the shields, and you can't use Disruption Field on it very well because of its k-back aura. With the latest pet AI changes, I think Ice could be a good match, maybe followed by Fire or Earth. It's a nice set although I still think Clarity should come much earlier. And Liquefy is only good if you have Power Boost tbh.
CoX 50s: <ill/rad> <ice/ice> <fire/kin> <grav/sonic> <ice/storm> <earth/kin> <kin/elec> <cold/psy> <thugs/dark> <fire/dark> <dark/elec> <night widow> <EM/ninj> <mind/icy>
Ice/Sonics is one I'm thinking about too with the new AI for jack. I think he'd look quite spiffy with the Sonic Shields and Disruption field running on him.
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Ice/Sonics is one I'm thinking about too with the new AI for jack. I think he'd look quite spiffy with the Sonic Shields and Disruption field running on him.
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This is exactly why I have an ice/sonics waiting at lvl15 (waiting for wen i finish over on the red side!) Hmm, could be good for task force omega...
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Sonic shields on jack always looks like he is about to melt ^.^
Level 35 Earth/Sonic Here.
Soloing is painful, although Sonics mighty -res powers help.
Mr. Poo now has 80% Res to Smash, 100% Res to Psionic, 90% Res to Everything else. Enough to make a Granite Tank weep 
He is a bit more keen to run in and grab aggro these days, making Sonic Disruption feild a handy effect to put on him.
Not there yet, but I imagine Earthquake/Volc Gasses/Liquify could create a horribly nasty zone.
Deleted my Grav/Sonic, mostly for concept reasons. Wormhole onto Liquify would work well, but Sonic Disruption did not go well on a Pet who knocbacks everything.
Just my 2 inf.
Hmm...
I was gonna roll a new controller....illusion/sonic sounds interesting...I was gonna go for something very "different" to previous sets and this sounds like (although I was a FF before)
I have an ill/Sonic and I only really enjoy the sonic part, should have remade her while she was a lowbie but there was I thinking that everything would be ok once she had tons of pets, the only shining light is her most recent power - liquify - is lots of fun
I have seen very few /sonic trollers on my travels and just wondered why. Its a set I've been considering but can't really decide on the primary. Probably mostchanceof me making an ice, earth or fire /sonic. Thoughts on those pairings and any others appreciated.