The XTS is a weak effort..it's based on the LaCrosse platform (Epsilon II)....the wheelbase is 4 inches shorter than the DTS, which was a decent car, though FWD. The XTS is tall, narrow, with very short front and rear.. The XTS is going to have a 4cyl as the base engine next year I've read.
I like my STS (RWD, V6)....if I replace it with another Caddy, I'll probably go for a CTS. Though I like the Chrysler 300 quite a bit.