I'd go with the Third Model Dragoon, I'd like one, but due to it's weight it wouldn't be very practical (as if that matters!) for field use, so that's why I've never got one. If I still had horses I'd have one for sure. I'd put one on my dirt-bike, but someone would pinch it. I'd have to hide it in the bushes every time I parked the bike. (in the mountains, not around town!) Having said all that, if I ever purchase another BP Colt, it will be the third model Dragoon.
I think the Walker is kind of ugly. No, I think it IS ugly. Too much of a good thing. The frame and cylinder is out of proportion to the handle/grip, and the bulbous rammer looks weird, besides being problematic and dropping with recoil all the time.
The ROA is a great gun, but...I don't know, "too modern"? I almost got one for my first pistol, (did have a junker .38spl before that) but wound up with a SBH, which I never regretted! Anyhow, the ROA is cool, but the cool factor on a Dragoon is through the roof. The ROA is kind of like a bat, compared to the Colts and Remingtons. It's neither a rat/mouse, or bird.