I've played a 5e campaign using Fantasy Ground. It shows a lot of potential and is about 70% towards realizing it. It's got a nice powerful language and it does so much nicely to take the load off the DM. Things would just work most of the time. And taking the load off the DM was even more for published adventures where you could already have everything in. It's good for the rest as well - images, shared notes that any player can update, etc.
On the other hand, it's expensive, has a steeper learning curve then it should for some things, and a lot of the mechanics you could buy and have the text but the mechanical part wasn't coded when I played. And some of the things would need a language expansion to code correctly. For example, it couldn't handle a paladin aura to automatically add +CHR to ally saves within 10', nor could it specify if damage was from magic for my oath of the ancients 7th level aura. So those always took DM modifications, often to back off half of auto-applied damage to some PCs. Which was confusing because you needed to know where it would handle everything and where it wouldn't and you needed to manually audit the process.
I haven't used Roll20, but it was talked about as the superior option for rules back when we were playing 4e online using maptools. We handled all the mechanics ourselves, but even there things like the fog of war for what each player could see with Roll20 was really tempting.
