Sorry to hear about your car getting totalled, never the preferred way to say so long to a car! Given that you drive 25K/yr I'm guessing you must have had over 200K on it. Was it relatively reliable, how did you like your 2006 Volvo?
Maybe it was a typo, but you're certainly not going to get a new midsize sedan for $16,000.
Volvos don't have the best rep for reliablity, but the 2nd generation S60 isn't too bad - Consumer Reports gives S60s pretty good marks starting in 2013. So if you really liked you 2006 S60, updating to a newer one might be the way to go.
Audi A4 gets better marks except for 2014. The 2.0T has lots of energy, nice materials and workmanship, and it also would use the least amount of gas of any of these. Most are AWD - but if you don't need AWD and you can find a FWD model, they are often relative bargains on the used market.
Subaru Legacy 3.6 is also another excellent car, especially if you live in the snow belt where AWD is a plus. Although CR rates it a little lower than Audi for reliablity, there are lots of late model Subies with high miles on the road. Overall, I think you would find the ownership cost of a Subaru less than the Volvo or Audi.Depending upon your market, you might be able to find a 2015 with Subaru's excellent suite of safety features in you price range. You don't mention safety in your list of gotta haves, but in your price range a 2015 Subaru is going to win in that category.
One car you didn't mention is the Mazda 6. This is an often overlooked, non-cookie cutter that is a fav of many auto journalists includng CR. M6's get good MPG and are quite reliable. They are a little less refined and powerful than the others, but have a unique fun to drive factor -- think zoom zoom. Here in the Seattle area, 2015 & 2016 models are available in your price range. This may be the best bang for your buck both in terms of intial cost and overall ownership cost.
Based on your description, I think the A4 FWD would be your best bet followed by the Mazda 6, Subaru, and last but not least, the Volvo. Best recommendation is to give them all a good look to see what seems best for your family, clients, and you!
As alway we'd love to hear what you choose and why.