I had a Cobalt I really liked, I think they are great for cheap, reliable transportation. They ride nice, fairly quiet, the 2.2 has a good amount of power and gas mileage is nice. I wasn't a fan of the armrest/center console, and I think the backseat was a little tight. I'd pick up another one in a second.
From what I understand, they have two issues - shift interlock switch on automatics, and the EPS motor. Both are cheap and easy DIY repairs. The powertrains and everything else on these cars are rock solid.
I prefer the Cobalt over the Ion due to styling, and I would avoid the CVT. I think the mid-cycle refresh on the Ion came in 2006, which made the interior a little less goofy and switched to a conventional 4 speed auto.