Go with the Mazda 3. Im sorry, but the Ford Focus is poorly designed. (Not unless your in Europe). But since the economy is doing bad, you might be able to get the Focus for a steal. The Mazda is pricey, but in my opinion I would get it over just for the fact its japanese and they build reliable cars. Ford not so much.
The focus gets EPA est mpg: 24 City/35 Hwy (manual) EPA est mpg: 24 City/33 Hwy (automatic).
All the model trims below "s Sport" get 25 City/33 Hwy (manual) and 24 City/33 Hwy (automatic).
s sport and s grand touring get 21/29 (manual) 22/29 (automatic)
For a sound system, the Mazda 3 has got what you want. BOSE surround sound. Best sound equipment company, i think.
Now for interior, i will have to say that the Focus is pretty nice
The Mazda 3 is nice too, but its all about preference. Its got red lights on gauges
Mazda 3 also has more standard torque and horsepower. 148 hp appose to 140 and 135 lb-ft of torque compared to 132lb-ft
The Mazda 3 has more passenger volume by .7 in
The Focus has more cargo room by 2 in
Keyless entry and start available as well on the mazda 3 and not on the focus
Visit mazda's official site and you can compare the mazda 3 with any other car in its class.