I haven't played two-handed, but I do find that the one hander is great for hitting with massive top spin which brings the ball back down quickly and gives you ridiculous angles. A short ball to a one handed backhand spells trouble, even if it's low.
Going down the line, without having ever tried the 2 hander, it seems more controllable with one hand, because the shot doesn't require core rotation, so less can go wrong. And you're right, the added inherent topspin helps there too.
The issue is whether or not you have the time to set up properly, it seems to take longer to get into position for the one hander, so early footwork is essential.
Also, slightly off topic, but I read somewhere that we all have a dominant eye, and ideally you should set up with that side closer to the ball. With the one handed backhand, you have no options, if you're right handed, you need to be right-eye dominant, otherwise you'll have trouble with the shot. Even more so when you get a crosscourt ball and wanna send it down the line, then your stance is even more side-on to the incoming ball.