Since I've never used Fantasy Grounds I cannot comment on its quality.
As for alternatives, RPtools are rather popular and free.
I have RPTools, FantasyGrounds and kLoOge. RPTools is excellent, not to mention free - and is currently my PFRPG DMing tool of choice. FantasyGrounds looks excellent, and plays well too - but there are too many idiosyncrasies for me to choose to DM with it (I play in a 4e campaign in it).
kLoOge is an old favourite, but with rather a steep learning curve. I would probably say it's the most powerful and customisable.
In short then - choose RPTools if you're just starting out and aim to keep most if not all of the character info separate. It can accommodate a lot of customisation, but not in an easy way. It's an excellent mapping tool though - especially if you're into dungeons and lighting!
I use FG extensively for Pathfinder and Rogue Trader.
It works very well in my opinion, and requires much less work in preparing compared to some other tools (I prefer to prepare very little within the program itself).
It looks and feels better IMO, though it has less fancy stuff like macros and "automated" lighting.
There are now also modules with the PRD rules available which makes it even better.
The 3d dice give a nice touch even though I never roll "by hand," preferring to use the /die command or double-clicking where available.
There are some flaws, particularly concerning connection details, but they're in the process of improving that.
Well worth the money considering the hundreds and hundreds of hours I've spent with the program for the past three years.
There are some other threads here giving a better comparison between the available VTTs if you search for VTT/virtual table top/maptools/fantasy grounds and so on.