While the CTS is the darling sport sedan from Cadillac, the STS was a more refined car with more room, and power (with the NorthStar V8) and better egronomics with regard to the memory seat and wheel recall functions. We have both a CTS (2008 premium ed) and an STS (2009 Platinum ed), so can compare them both. We also had a 2005 CTS and two (still have 1) LT1 Fleetwood Broughams, so we've had a few Cadillacs in recent years
Handling and performance are equal to or superior to the CTS, particularly with NorthStar & the wide 255mm 18" rear tires (CTS has 235mm front & rear) Interior room is better and the single glass sunroof is quieter.
15 speaker Bose system is very powerful and clear.
This car is a great road car with all the power you need to take on all challengers. Bought mine used with low miles from a man who meticulously kept it in pristine condition and I intend to following his footsteps.