I wasn't aware there were so many VTTs - yikes! I only knew of 6 of those and of them, have only GMd with 3. I've gotten familiar enough with the 3 I've used (Foundry, Fantasy Grounds and Roll20) that I can succesffully run a campaign with many features enabled with any of them. What I use is heavily driven by costs.These days I'm only using Foundry and Fantasy Ground Unity, because the 1-time purchase licenses I bought for them are considerably cheaper that the annual subscription fee I'd need to pay for Roll20. I'd never be satisfied using a VTT without the ability to customize character sheets and without a customization API, so for Roll20 I need to go Pro which end ends us costing me $135/year in my country's currency; as much or more than what I paid for perpetual licenses for Foundry and Fantasy Grounds.
I tend to use Fantasy Grounds Unity more than Foundry, because I can buy my DLC via the Steam store. Buying that way always ends up being cheaper than buying direct and cheaper than the equivalent modules on Foundry or Roll20's stores; something to do with how Steam handles the trade laws & conversion with my country's currency. Not to mention they frequently have sales where FG DLC is discounted across the board. I also find customization for FG to be more feature rich and easier than doing the equivalent for Foundry.
Where I'm biggest on Foundry is for D&D 5e and The Dark Eye campaigns, the latter being a TTRPG that isn't available for FGU. My 5e players and I also use dndbeyond.com and we like the freebie Beyond20 chrome extension, which allows players to make real-time rolls from their dndbeyond character sheets instead of the Foundry sheet; also works for Roll20. All my 5e player prefers PC creation and the character sheets at dndbeyond, so using Beyond20 with Foundry is a good fit.
My biggest dislike for FG is the need for players to download a client-side app. That said, the app takes up little HDD space and I've yet to have a player not successully insatll it; including one that installed the older Fantasy Ground Classic app on Linux. The newer Fantasy Ground Unity client has versions for MAC & Linux, so installs are easy on those OSs. Still, it's definitely easier for a Foundry player, who just needs to connect their web browser to my server.
Initially, my main reason for going with FG was the solid implemention for Savage Worlds (one of the 1st on that VTT), but SW DLC for Roll20 and Foundry have since evolved to equal it. For FG, I also own and run campaigns with Call of Cthulhu, Traveller, 13th Age, Old School Essentials, FATE Core (provided for free), Pathfinder 1e (provided for free) and the Cepheus Engine.
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