I would not own a reader without a cover, so I always consider weight including the cover. Size, too. And width is the most important to me, as that is what allows easy fit in a pocket. The 350 was a perfect size for me. The T3 with cover is even less wide than the 350 with cover. That's because there is no cover overlap on the T3, while there is on the 350.
Also, IMHO the Sonys just look and feel great. With no software glitches.
And I don't have to deal with any silly side lights. (Uh-oh. THAT should get some people wound up!
)