I have a PRS-T1, and made the decision to get a Kobo Glo. I've now passed my Sony to another family member and kept the Glo.
All the books I had on my Sony transferred easily. I've never used the Sony store either, and have books from a variety of sources and book sellers.
My main decision to go for the Glo was the in-built light. Much of my reading is done in bed, and I hated the glare off the Sony cover light and the constant re-positioning of it. I do like the light on the Glo for its even coverage of the screen. It should save me having to make sure I always have a stock of AAA batteries too. I find the screen background on my Glo is slightly whiter than the screen on my Sony, but the difference isn't huge.
I've had no problems with the fonts on the Glo. I do miss the definite sizing on the Sony -the graduations on the PRS-T1 make it obvious what size you'll get when you touch the screen, as opposed to the sliding scales on the Kobo. The Glo does seem to take a tiny bit longer than the Sony to change the fonts. I've not noticed any issues with the font rendering on the Kobo - all the words seem a uniform colour and 'thickness'.
I do miss the dictionaries on the PRS-T1. The English dictionary that comes on the Glo isn't terribly comprehensive.
The screen texture of the Glo is 'rougher' than the smooth glass of the Sony, but it also seems to be less reflective. I hate the feel of the Glo screen that much I've taken to tapping the screen rather than the swiping I did on the PRS-T1.
I also miss the ability to download library books straight onto the Glo. I read those a lot, and to have to make sure I connect up to ADE before reading will be a minor irritation.
Overall, I like the Glo very much. It's got some quirks that I'll need to get used to, but I'm happy with it.