I am biased, since I am one of the owners and developers for Fantasy Grounds, but here is why I think it will fit your needs best.
While it supports play for any game system, there are fully customized and licensed rulesets for both Savage Worlds and Call of Cthulhu available. Each of these each have a ton of additional licensed products. You can always manually input stats and so forth for a given Savage Worlds or CoC adventure module if you have them, but it is nice that you also have an option to buy a fully pre-made and 100% converted version for a very large number of them.
The full SRD for D&D 3.5 is also included and the rules are supported for both 3.5 /Pathfinder and 4E out of the box if you don't mind entering in stuff not in the 3.5 or PF SRDs. Finally, there are a number of 3.5/PF compatible modules available from a couple different companies, such as Expeditious Retreat Press, White Haired Man and Malhavoc Press (Monte Cook's own company.) Disclaimer: There is a new conversion from Malhavoc Press, but the others we have available are some of the earliest conversions available and not quite as nice or easy to install as the latest. New conversions (from 2009 on) have simple installers and don't require you to follow a README.txt that tells you where you need to put everything.
The community is very active, as I expect is true for MapTools. They've made a large number of rulesets available as well. The major limitation here (for Maptools and FG) is that due to legal restrictions, they simply cannot contain all the actual imagery and content that they could if they were a licensed product. By taking an active approach to license products and paying royalties to publishers, we think this helps the gaming community over the long term more so than a collection of only freely distributed content. Our 23,000+ licensed users seem to agree.
I know I am going to come across sounding like I am knocking Fantasy Grounds, but here is why I do not buy FG, or BG.
You talk about licensing. Well, I already own a ton of adventures. So I have already paid my dues, so to speak, to all the gaming publishers. So when I want to run something I either scan in the relevant maps, or use the PDF copies I have of the relevant adventure. Or, I use all the tile products I have bought, and in many cases scanned, because a PDF version was not available. So between all of the resources I already paid for, I can put together my own modules, built precisely how I want them built. Then with some sets of Campaign Macros, I can easily make the rolls I need for monsters and NPC's.
So sure, if someone has money to burn, buy Fantasy Grounds, or Battlegrounds, pay you guys to save people some time. I don't have money to burn, so I build my own stuff. My gaming group does not have money to burn, so we play Maptools. This way, I burn all my money on RPG companies and the print/PDF products they produce. Which is my licensing.
So thats why I go with Maptools. I find it easy, gets the job done, and lets me have money to spend on other gaming stuff.
But if I had money to burn, and didn't have or want to take the time to create my own Macros and set up my own adventures, and wanted everything to look as pretty as possible, I'd invest in Fantasy Grounds, or maybe Battlegrounds. But as it is, Maptools allows me to do what I want, and for free. Plus its licensed. Since I use stuff I bought legally, and for personal use.
