Hiya.
I own both. My 2¢ is this: If FG has the "frameworks" for the games you will be playing, it wins. If FG is missing some of the "frameworks" for the games you will be playing, it looses, so go with BG.
I find FG's 'interface' to be much more pleasing on the eye for long periods of time, and being able to chance the general color tone of everything ("day", "night", "campfire", "underground", iirc), can really help relieve eye-straine as well as promote a certain 'feeling' for encounters and areas. What I find the all time BIGGEST pain in the rear with FG is that, unless you are a programmer or have weeks to learn how to use xml...you pretty much *can't* add any new game system framework, or seriously tweak the ones you do have to fit your house rules. There was a rumor floating around (havn't checked on it in about a year) of someone doing a "GUI" for a tool that would allow someone with little knowledge of programming/xml to basically 'build' his own rule set or at least tweak the ones we do have...but so far, to my knowledge, this has been just wishful thinking.
Battlegrounds is just an all-around great VTT. It has options that make it very versitile for just about any game system out there...square or hex grid. Last time I checked FG was "square grid only". Battlegrounds also seems to be able to impliment user requests and changes much faster than FG can/does. I'm not keen on BG's dice stuff, but you can get used to it. So, if you have a lot of other games not 'covered' by FG, Battlegrounds is the way to go.
As for MapTool...it's nice. I do like it quite a bit, but there's just something about it that feels..."cold" to me. I can't put my finger on it. *shrug*
^_^
Paul L. Ming