I'm not trying to start a war here, just wondering what your takes are. They pretty much have the same concept of lightweight desktop, but with different toolkits.
I'm a KDE person myself, but I've had experience with XFCE.
I've tried LXQt in the past but never really gotten into it, perhaps the timing was just not right.
I liked Xfce a lot, and used it for more than a few years, until it migrated to Gtk 3. (Modern Gtk breaks things that I use, and forces UI decisions that constantly get in my way. It's just not for me.) It has also become more memory-hungry over the years, so is no longer quite the lightweight desktop that it once was, although that's not why I switched.
LXQt was first on my list when looking for a replacement, but I used it only briefly, because there were too many rough edges and little integration problems. It didn't feel like a cohesive desktop compared to (old) Xfce. I imagine some of that was a side effect of ongoing work to transition away from Gtk. It was a couple years ago, so it might be better now. I still love the idea of it.
I feel the same, though having more options for lightweight DEs is better. I came from gnome 2 after Ubuntu switched to Unity DE back in the day. Xubuntu ran nice on all of my kids low power devices and it became my desktop as well ever since. It's just as happy on my work laptop as well as Ryzen thread ripper with 3 rtx4000s and 3 magewell hdmi capture cards we use for visualization at work too. It really feels like a solid DE with less fuss than most.