I've used Roll20, Foundry, d20pro, Fantasy Ground (Classic and Unity), Role, Astral, and good old Map Tool. I've loved and hated them all.
As a player, I really like Roll20. It's find-a-game system has been a life-line to the hobby during my long stints overseas. It works from every country I've tried it and is generally stable, even with crap Internet connections. But as a DM, I hated prepping games with it. First, I was trying to prep a mega dungeon with hundreds of maps, and even at the expensive subscription levels, it couldn't handle the data sizes. Second, I find map prep with it inconvenient. Third, there is very little customization you can do with Roll20.
I really made the college try with Fantasy Grounds, because I wanted to have as much of the work done for running D&D games done for me and nothing matches FG for that. But I couldn't get the game server to work from the mid-east without a VPN and over less-than-great internet, I had enough trouble downloading the assets in-game as a player. There was no way I could run games as a GM. Further, I really didn't want to have to carry two computers around, but couldn't install games on my work computer, so having something hosted made more sense.
That's also why d20pro was a no go. Even though I like its simpler interface and decent support for 5e.
I ended up with Foundry, hosted by the Forge. What I love:
- I can take my license and go to another hosting provider or host it myself if I ever want to.
- My current hosting provider (The Forge) offers good performance, great service, and a decent price. Any assets you download from their Bazaar doesn't count towards your storage costs. At my subscription plan, I've been able to load a lot of data in terms of hundreds of maps, thousands of tokens, world anvil content, and D&D Beyond content.
- There are so many community developed modules that allow incredible customization of the platform, more than any other VTT.
- I'm able to bring all my D&D Beyond content into it, so I don't have to pay for it a third time to use it in my VTT
- I'm able to bring in content from World Anvil
- Prepping maps for dynamic lighting, etc. is the easiest of any VTT I've used. I actually enjoy it now.
What I hate:
- Because there is no official WOTC license with professionally prepared assets, everything is based on community developed game systems and modes. I still don't have things set up the way I want so I can just do everything in the VTT and I still primarily use it just for map display, fog of war, etc.
- The trouble with moding is that some stop being developed and some conflict with each other. Maintaining and futzing around with Foundry becomes another hobby onto itself. If you are the type that liked moding Skyrim and other PC video games, you'll probably love Foundry. If you play your video games on console and want to just sit down and play, then Foundry will be frustrating.
WITH ALL VTTs, I find the best experience is when you can buy an adventure that is all pre-prepped. I've run some adventures prepared fully by other people and it was amazing. But my main campaign is not available all prepped on any VTT that I'm aware of. So I never use all the bells and whistles of any VTT because it is just too much damn work to prep.