I have a 2011 Impala car provided to me for my business travel.
The Impala is over 5" wider than the Sonic - and that translates into 5 extra inches in both the front and the back seat area.
The trunk is cavernous - I frequently carry a wide assortment of sales literature, demo product and actual product for delivery to my customers.
The fuel mileage (3.5L V6) is very good. I average about 30 MPG overall in my sales travels. I usually drive about 1000 miles per week, some Interstate, some 2 lane highways and then driving around in the towns while I'm making sales calls.
Currently have 118,000 miles on this one. Very reliable.