I will most likely trade it in, unless the trade in price is low, then I will sell privately.
I love the Triumph, but it time for a change...
I always trade because I'm too impulsive/lazy to take the time and effort to sell it myself. And I don't ride anywhere near enough to justify more than one horse in the stable at a time. Not to mention the hassle of dealing with the flotsam and jetsam of humanity that could come answering an ad at any time. When you trade, for the difference in what you could get if you sold outright, you get to drop off the bike you no longer want and drive away on the one you do want, end of story.
I really like the Thunderbird, too; it was probably the most un-Harley cruiser available at the time, it's smooth, gobs of low-end torque, comfortable, and handles well for a 740+ lb bike. Oh yeah, and a great looker to boot. But I don't think it's displaced the VTX1800 as my favorite of all the bikes I've owned. And I've only put a sad and sorry 2,200 miles on it in two seasons. If I could design exactly what I want from the ground up, the CTX1300 is that bike.