Been meaning to get foundry since there is a pretty powerful D&D 5e script for it, but the prospect of learning another platform is a bit daunting.
I have been using roll20 for nearly 6 years now and while I recognize the code is a hot mess, performance is trash and one of the owners is a power tripping cunt who will ban you merely for having a similar name to another user they banned, it still works for what I do.
Lastly I've heard it is not so great for systems that aren't d&d 5e, for example they had trouble adding character features or spells which savage worlds uses, but I suppose it will be much better once someone builds a module for the system in question.