I can't speak to the CTS-V Sport, but I will say, a lot depends on your desires. Yes, driving them is paramount. One thing you're also asking is chosing between a coupe and a sedan. So that's a little confusing from the get go...
If you're into more of a "hot-rod" and want to modify things, the CTS-V is unquestionably the king in this capacity. If you want something a little more "mature", the STS-V may be your choice. Also keep in mind, these things (STS-V's) are getting older and are going to be more prone to issues and parts aren't as easy to come by. Being a Supercharged N*, yea, you're gonna be planning maintenance/work on them a little more... The CTS-V is newer and using a GM small block V8, parts are going to be more readily and easily available.
If you're into more of a "hot-rod" and want to modify things, the CTS-V is unquestionably the king in this capacity. If you want something a little more "mature", the STS-V may be your choice. Also keep in mind, these things (STS-V's) are getting older and are going to be more prone to issues and parts aren't as easy to come by. Being a Supercharged N*, yea, you're gonna be planning maintenance/work on them a little more... The CTS-V is newer and using a GM small block V8, parts are going to be more readily and easily available.
