Well the Avalon IS considered an old person's car (I should know, my grandparents drive one -_-), so that'd be best suited. As for performance....mmmmm......no....My gp's have an Avalon Advantage with the questionably "powerful" V6...the CTS would eat it for brekky. Hell, my R31 Skyline is quicker and thats 15 or so years older and it has less power. But anyway.
Comfort = Avalon
Style = CTS
Performance = CTS
Function = CTS, its a newer car and it has more kit.
Toyota Avalon XLS or limited by far. many more options, power, reliability, nav, 280HP and 315 torque, 24 MPG and only 38,000 maxxed out. Fast and comfortable with more bells and whistles then others.