I own a 2008 Dodge Caliber 2.0 Liter SXT (automatic), and drove a 2008 Avenger when my Caliber was in the shop (got hit by a snow plow). Chrysler was not my first choice in a car, but my father in law works at Chrysler in Brampton Ontario and he bought it with his employee discount. It's hard to say no to a brand new car for $12 000.
Anyway, the Caliber isn't a van and can't be compared to a van as some people have tried to compare it to. For a car, it is very roomy with ample storage space. All of the seats (except the drivers seat) fold completely flat which gives extra space.
I did not get the car sound proofed or anything additional done to the body after market. My car is not exceptionally noisy. You can hear the engine while accelerating, but it is not what I would consider too noisy. If the car is on and the AC off, it is hard to tell that the car is on. The AC unit is loud, but most cars have loud AC units. The Caliber is not a race car, it is not exceptionally fast, but has decent acceleration. It handles well in the city, highway driving is ok... it's fairly smooth, but I have driven other cars which are smoother.
I like the interior of the Caliber. All of the controls are right up front and centre, and easy to access without looking. Plus there is a 120v DC to AC converter so I can plug my computer in and use while riding shotgun. I like the cooler in the glove box, it is not overly cold, but will keep water or pop cold no problem. The ventilation system must be on for this to work which is something I do not like, though if I have the heat on, the cooler is blowing cold air which means they are not the same temperature.
I find the seats are very comfortable, with ample leg room. The floor has some weird 'box' like things which made finding floor mats harder. I don't mind the exterior. I like the boxy finish of the Caliber, but I find it only looks good in a few colours. I have a Steal Blue Caliber which I think the boxy finish looks great in. We also considered the classic Dodge red (which my wife vetoed against). We also looked at silver, which frankly looks horrid when used on something this boxy.
As far as the Avenger goes, I drove it for a week. It was the 2.4L model with automatic transmission. It was a rental so I drove it harder then I drive my Caliber. It obviously is much faster, and therefore much louder. I found it quiet when turned on without the AC on, but it was too noisy when accelerating. Even accelerating normally (without flooring it) was too loud for my tastes.
The interior was much larger and more spacious then the Caliber. However it was too flat for my liking. The seat was too close to the ground for my liking, and the gear shifter was level with the seat. The central panel with the radio and climate controls is nicely centered and looks classy at first, but after using it, it is easy to tell it is cheap. The climate control nobs are simply plastic with a chrome sticker on them. They felt cheap and were fickle to use. To adjust the fan speed or temperature, only the outside of the nob moved, the inside had the temperature and fan speeds printed on them. This made the nobs loose and made vibration sounds.
I liked the steering wheel. It had chrome finishing which looked classy and felt good. I liked the telescoping adjustment. The car handles well in city, and is very smooth on the highway.
My wife and I looked at both the Caliber and Avenger when we bought our car. Ultimately we went with the Caliber because it got better fuel milage, had a CVT transmission (you don't feel the car change gears it's amazing), it was smaller but still had amble storage room and seating. We both liked the interior better (especially the DC to AC converter), and the price was right.
It really depends what you want to use the car for. If you want performance, get the avenger. If you simply want a tool to get from one place to another with storage and seating, get the Caliber.
If we had to make the choice again we would have made the same one. It will be 1 year old on May 20th and we haven't had any problems with it at all. We put on just over 12 000KM, mostly in city driving. The Avenger was fun to drive as it is fast and has attitude. But it really wasn't practical for us. In my opinion, the Avenger is just a poor man's Charger.
EDIT: I forgot to add the part about the air bags. The Caliber has front air bags for driver and passenger, plus side impact air bags for driver and passenger, plus it has and airbag under the steering wheel to protect the driver's knees. I don't know what the Avenger has, but I do feel safe in my Caliber.
EDIT 2: Also, if we hadn't got my father in law's discount we would have got something else. Our car was worth $23 000 retail after we added some packages, but got it for $12 009. I would never pay full price. We probably would have got a Hyundai or a cheaper used car had it not been for the discount. I'm all for supporting the domestic automakers, but if they can't produce a quality cheap car, then I can only purchase what I can afford and the foreign automakers make cheaper cars.