Plenty of Kobo Touch users are perfectly happy with their Kobo, but a 2-year old device versus one that's just been released? Unless the former is a fair bit cheaper, I'd be snapping up the T3. (Here in the UK the Kobo Touch has been reduced to £30-£50 - at £30 I'd buy it over the £99 T3
), but at the same price, there'd be no contest.
If you aren't interested in a lighted reader (Kobo Glo or Aura?) then I'd take the T3. You will have more font and text customisation options with the Kobo, but the T3 has increased screen resolution & faster processor. Page turns, book selection etc will all feel a lot faster. And if you are borrowing from a library, the Sony's have a slight advantage in that you can browse from your ereader and borrow directly from the library - every other reader you have to borrow library books via your computer then load them onto your reader (only a plus if thats a feature that might interest you).
I'm also not sure what the negative reviews are of the Sony, they have generally been pretty solid, their firmware tends to be a lot more robust than Kobo. The criticism of Sony has been that they don't seem to be putting the same effort into their ereader business, and have lost a lot of ground by not competing with Kobo & Amazon with a lighted reader.