I've got both and they're both great pieces of kit but I think I prefer the Tornado T to the ego-C because of its simple 3 part design. The ego-C has 5 components and it's just a little bit more hassle to take apart and clean or re-charge. I've also experienced more leakage from the C whilst the T hasn't given a moments bother.
As far as performance goes, maybe (only maybe) the ego-C has the edge but it's next to unnoticeable to a novice like me. I've found that I can change flavours on the T and in a few minutes there's no hint of the previous mix but the C seems to cling to previous flavours for ages.
The C has the advantage of cheaper atomizers but as my T atomizer just seems to last and last I don't know yet if the overall cost difference is that great.
If you've been happy with the Tornado T, personally I'd stick with it. All IMHO of course.

I understand the choosing which Tornado to go with is strictly preference. Honestly, the eGoc is by far the best product on the market. The leaking that I've come to figure out is due to the lack of design from the actual tanks. I haven't had any leaking problems unless certain tanks are in use. As for the change of flavor, it's almost instantly. The trick is to fire up the atomizer for a few seconds and let it burn. Then you place the tank in, take two slightly deep hits without the use of the battery and then you're ready to vape. Cleaning the atomizer on the c is a lot easier. I don't understand why the C wouldn't be an upgrade for you. As I stated, it's all preference. Honestly, common sense tells you the C is by far the best to vape with.
Stay away from:
Clearomizer's
Tankomizer's
Triple Coil Cartomizer's (no leaks but no hit)
I'm not sure with the Duel Coil Tanks because I haven't used them. I ordered mine today and hopefully there's no leaks. I could honestly say I've lost around $100 due to the leakage of tanks.