I would suggest taking a look at the following-
2008-2010 Kia Optima (4-cylinder)
2007-2010 Hyundai Sonata (4-cylinder for best fuel economy, but V6 gets decent mpg)
2009-2011 Mazda6 (4-cylinder)
2008-2009 Subaru Legacy (non-turbo 4-cylinder)
2007-2011 Nissan Altima 2.5S or 2.5SL
All of these have good fuel economy, above average reliability history, comfortable interior and nice ride quality. I particularly chose these mdoels because the car will eventually be passed down to your teenager. All have HIGH frontal, frontal offset, side impact and overall crash test ratings- so they are very safe. All of them have more than adequate acceleration and overall performance, but not excessive amounts of power that could be dangerous (or lethal) in the hands of a teenage driver!
My personal pick would be the Mazda6 because I love the styling and the front seats are the most comfortable, supportive ones I've experienced this side of Volvo. The Subaru is the only one that features AWD (All-wheel drive) which would be an advantage in northern climates. But the AWD also adds weight and increases friction, so the Legacy 2.5i is also the slowest of this group and fuel economy is nothing special.