They are different services which are intended to do different things.
I've been using D&D Beyond for a couple of years, as both player and DM. I've been using roll20 for a couple of weeks. I own many books offered through D&D Beyond, but not on roll20. So I can't offer direct feedback on every feature roll20 offers in this area, but the reasons I ...
I've run several games for friends who live in other cities on Roll20 and the current campaign I run is there. There are more pros and cons than this but as you only asked for two, here they are:
all the important features you need to play are free and if your DM does decide to pay, everyone in the game can see the paid features like tokens and ...
The page settings allow you to set grid size and scale
By accessing the options for each page, you can set the grid size and scale:
Access the page settings:
Then change the grid size:
If you have a map where roll20 is interpreting the 10 ft squares of the map as 5 ft, you can either increase the "1 grid cell" setting to 10 ft, making all squares get ...