I have played with the VTT very briefly, but it was some time ago and it's possible it's improved since then. I'm a newbie DM though, and I'm currently running a campaign using Maptools.
VTT (when I last played with it)Con: I didn't see any way to drop in my own custom images for mapmaking and such
Con: No lighting/vision blocking/etc tools. Wandering around in the dark and tracking what players can see is complicated to do at a real tabletop but trivial when a computer's modelling things, it seems silly not to take advantage of it
Pro: Trivial to get a player's stats from a dnd4e file or a monster's stats from adventure tools imported
Pro: Fast to set up.
Also, I do recall having the ability to invite non-DDI subscribes to VTT (though they don't have access to adventure tools/character builder to import their own characters so you'd have to do it for them) -- so it does NOT require everyone to have a DDI sub, just the host.
Maptools:Pro: Extremely customizable (Maptool is designed to be system-agnostic, whether you're playing D&D4E or running some war simulation game on a map that uses hexes in a battle system where the direction a character is facing has a significant impact.)
Pro: Wide existing userbase. For 4e, you can download your choice of a small handful of "frameworks" that define common macros and easy-to-use interface for your campaign. (Or you can be minimalist and track everything yourself -- or something in between.) I use a framework[1] that gives my players an interactive character sheet that lists all of their powers, and they can use a power, select its target(s), check boxes for combat advantage/charge/cover/etc, and it'll do the relevant rolls with all of the correct modifiers.
Pro: You can make your own maps in Maptool (though if you want really pretty maps, your choice of painting program is likely a better choice). There's a huge set of user-created contributions for terrain, objects, dungeon dressing, etc. -- I've made some myself[2]
Con: Maptools versions are not compatible with each other, so you must ensure your players all use the same version you do or Bad Things(tm) can happen. Maptools is also not currently compatible with Java 7, though the next release should resolve that and it's not too difficult to force it to run on Java 6 if you have both versions installed. [EDIT: VTT is currently not working in Java 7 either, based on some other posts on this forum.]
Con: Maptools needs to be installed. VTT is pretty much self-installing.
Pro: Real-time lighting and vision-blocking/fog-of-war. Con: Doesn't support 4e lighting rules (Brightly Lit, Dim Lit, Darkness) -- your choices are 'can see it' and 'can't see it', though you can fake it to some extent.Vision blocking can be slow if you make it too complicated.
Con: Maptools is not designed specifically for 4e, so is not as polished at handling 4e and typically slower to update to 4e rules changes -- though often times you can fake it enough. For instance, the framework I'm using doesn't directly support things like Sneak Attack damage, so my rogue player just codes Sneak Attack as a "no action" "special" power that has no attack roll and rolls the correct damage dice. Augmentable psionic powers aren't directly supported, but a power can have a power point cost and you can make multiple versions of a power to handle it.
Re Maptools networking: In my experience, it hasn't been too difficult to set up (but I'm technically inclined and run custom firmware on my router) -- though your options are
a) Your DM must host, or
b) Your DM has to trust the hosting player with his campaign file, or
There is a way to create a 'campaign repository' of objects used in your campaign using your choice of web hosting -- clients will try to download assets from that repository rather than from your PC which should alleviate network concerns. I haven't personally used this feature, however, so don't know a lot about it.
Maptools also has valid use for an actual in-person game: DM runs two copies of Maptools on his laptop; one runs the server and the DM view, the other connects to the server as a player view and is on the laptop's "second monitor" (big screen TV or a projector setup). I don't think VTT has that functionality.
If it's not obvious, I'm a fan of maptools
[1]
forums.rptools.net/viewtopic.php?f=58&t=...[2]
forums.rptools.net/viewtopic.php?f=8&t=2...
