I would try to test drive each one of your picks. I have an 06 STS-V and it is a great cruiser, comfy and on the quiet side. HWY MPG's are around 21 to 23. no problems with mine but it only has 30K miles and it is listed in the classifieds here for sale.I’m looking to buy a car and I see that all of these cars a prices around the same and I was wonder which one would be the better buy In Terms of reliability, speed, fun to drive, and the most unique
I also have a 2014 CTS V-Sport and it has been a great all around performer and no problems. HWY MPG's are from 27 to over 30. Just got back from a road-trip and got 28.4 mpg and that was having some fun too on the twistys. More nimble and lighter than my STS-V and more modern good on a track too.
CTS-V would be the fastest, but of course cost more. Go for test drives