I personally have never understood the appeal of Roll20. I've never used Fantasy Grounds, so I don't have that as a comparison, but I find Roll20's user interface / user experience to be clunky at best, and nigh infuriating at worst.
When I discovered Tabletop Simulator on Steam, it was exactly what I was looking for. I don't need my virtual tabletop to be an information manager, character builder, knowledge repository, or combat tracker.
I just need it to clearly define a map space / battle mat, with easy-to-interact-with components that can be quickly updated and manipulated on the fly, in a way that most closely resembles a "real world" battle mat, but without having to drag around hundreds of mini-figures or standups.
I'm guessing the reason it's not mentioned more frequently around these parts is because it's not free. But Tabletop Simulator's $20-per-participant price point provides a 100x return on investment over Roll20's "free." And there's enough free models, mods, textures, map images, pre-built scenarios, and more, that I can't imagine anyone needing to spend more than the initial $20, ever. Need a new battle map? A 60-second pinterest search is about all it takes to find something usable in TTS.
Like anything, there's a few things to get used to in doing basic battle mat setup, but once you grasp the basics, it's simple and takes only 5-10% more time (if that) than setting up a physical battle mat scenario.