2.2 or 2.4
#2
No complaints with my 2.4, just be advised that they prefer Premium gasoline over Regular if fuel cost is a concern. Never have run mine on Ethanol due to the near unavailability of E-85 in this area, never made sense to drive 60 miles one way to save some bucks and get lower mileage on the "corn juice".
#4
The 2011 with the 2.4 just turned 9,000 miles, the 2007 is at 64,600 miles, and the 2006 is at 87,300 miles. No complaints with any of them, as far as economy goes there isn't any real difference between the 2.4 and the 2.2's. They all average out at a little over 32 mpg on the highway and 24 mpg in mixed around town driving. Premium fuel isn't required in the 2.4's but its recommended(they will run on Regular), tried one tankful of Regular and I did notice a lack of performance, so I went right back to Premium.
#6
I test drove both a 2.2L and a 2.4L when I was looking for an HHR. My impression was that the 2.2 seemed kind of slow and sluggish. I have the 2.4 and the amount of power it has for a 4-cylinder impresses me. My last car had a V6, but my HHR has almost as much HP as the V6 had.
I have 144,000 miles on my 2.4L engine, also.
I have 144,000 miles on my 2.4L engine, also.