I use Fantasy Grounds, and I would be unhappy to give up its ease and automation. It does have a steep learning curve, but once you become familiar with the program and its quirks it spoils you rotten. As people have said, the application and its digital tools are constantly being tweaked and upgraded to improve the user's experience.
Either platform will let you start for almost nothing. Roll20 starts free for the most basic functionality, while subscribers get "bells and whistles." The free version of Fantasy Grounds will let you become familiar with the software and connect to a host with an "ultimate" license, and comes with the 5e SRD and basic rules packages included.
Where Fantasy Grounds really begins to shine for the user who has the ability (or willingness) to buy the full 5e set of materials. These typically cost about as much as the physical product's MSRP, but often have a lot of functionality built in to support the automation Fantasy Grounds is capable of. For example, dragging a monster from the FG version of the Monster Manual onto the combat tracker (where initiative and hit points, etc. are tracked) will give the DM clickable abilities and a fully populated list of clickable spells or spell-like abilities, meaning you just need to target a PC and click to attack and again to apply damage. To achieve that level of ease-of-use from Roll20 requires a lot more set-up ahead of time.
That said, if you use a lot of home-brew material (classes, monsters, whatever) in your campaign, Fantasy Grounds absolutely gives you the complete freedom to set those things up yourself, and use them along side the "official" published materials.
Ultimately, either Roll20 or Fantasy Grounds will be a useful tool for your campaign. From what I've heard, Roll20 is probably a better choice for a digital tool to enhance your traditional coffee table game night, where your players want to roll physical dice and look at a paper character sheet. Both products are being constantly upgraded and driven by competition with each other, which benefits users of either.
One important thing to keep in mind is that neither of these platforms will transform your campaign into a video game. They're both virtual gaming tables, designed to facilitate and enhance the traditional tabletop gaming experience.