First off, anyone who knows me here on ENW, knows that I'm not argumentative nor am I trollish, so take what I have to say next is a completely non-confrontational way:
For me, it's a simple time vs money statement. I have very little free time as I'm a single dad with a teenage daughter. However I make a very good living and have the extra cash laying around to pay for fantasy grounds (though to be honest the buy in costs of Fantasy Grounds is fairly low: A $10 subscription and another $3 for the basic rules gives you everything you need to play D&D with your friends online as the ultimate license subscription means they don't have to pay anything. To get the full 5e rules can be seen as very pricey. I won't argue that. $50 for the full PHB and $50 for the full MM. However, those rules sets work very smoothly with the FG interface, I don't have to learn how to code/enter/what-have-you anything and (as shallow as it is) it looks pretty.

I plan on using FG to run 5e for years. That $100 over a year comes out to about $8.50 a month. So for 18.50 a month (though really it's $110 the first month and $10 every month after that), I get a nice looking VTT that works well, is constantly updated and bug-squashed, has a amazing support system of users and developers, and works very well for me, my needs and within the bounds of the amount of free time I have available to prepare, run and participate in games.
As a player, my costs would be even lower. As in free as long as the DM has the ultimate license and $4 a month if he doesn't. It's a very small out of pocket expense as a player and I can play in multiple games and game systems.
Roll20 is not without its costs as well. Dynamic lighting and line of site for example is NOT free. It requires a Supporter subscription and that's $4.99 a month though that is probably only on the DMs end of things (just like the FG ultimate license is only on the DM). For all the really cool stuff, it's a Mentor subscription for $9.99 a month. Then you need to take lots of time to enter things into roll20 which for some people (and there are lots of those) is a non-issue and worth the cost savings, however much that may be. I
don't have that time. So that is a huge cost for me. And it might be for lots of others.
I've played games on roll20 and I think it's awesome. No doubt about it. If I'm a player in a game, I have no qualms whatsoever in using roll20. As DM, I just don't have the time. Ok, I might have plenty of time if I were to use roll20 often and become polished in how to use it, but that would still take me lots of times because I'm not tech savvy and the simplest things can sometimes take me forever to figure out even with help.
tldr: In short, FG is worth the cost in money for the savings in time for me. Both VTT work wonderfully for playing with people over the internet. Neither FG nor roll20 is free if you go anywhere above the basics of the programs. I guess that's all I had to say. Except this: Good Gaming, everyone!