I have some of all three companies mentioned above, Fat Dragon Games, Skeleton Key and Worldworks and have been doing cardstock modeling for years. They all have their place at my table, I tend to play more miniature games with my stuff, so I use more of the FDG & WWG stuff. The FDG stuff is really easy to put together and inexpensive if you have your own printer. The WWG stuff is not any harder to put together, but I would not suggest it for first timers, not a knock, just an observation. My 13 year old son helps build alot of my terrain (slave labor is cheap) and he has no peoblems with the FDG stuff, but we are in the middle of The Maiden from WWG and he has had a few issues with it. I would definately recommend Fat Dragon Games to get you going, their price, quality and quantity of stuff you get can't be beat, after you get going you can make your own decisions as to which one suits you the best.
I definitely agree. I have some FDG and WWG stuff, and you pretty much nailed it. IF you are just starting out, definitely go with Fat Dragon Games. There stuff is clean, simple, and great. It's easy to figure out, easy to put together, looks great, and definitely adds alot.
The WWG stuff is pretty good. I think some of the texturing is better in some spots. I think their best stuff are there "set pieces", like the Thoumont's magic shop and the maiden. Really detailed and intricate. Looks real impressive when it's assembled, but not really versatile without alot of work "kitbashing" the stuff. Their "mix and match" utility sets are good, but I'd have to go with Fat Dragon for the most utility stuff.
To clarify, I'm currently using the WWG "Thoumont's Rare Tomes" magic shop as the "headquarters" for my party. However, they just entered a goblin controlled dungeons, and I'm using the FDG EZ-Dungeons for all the dungeon work. However, I prefer the WWG caves style for the cave sections. Then again, I also use the FDG Dragon Tiles: Taverns. So I'm all over the place.
So, typically, I find the Fat Dragon Games products to be overall simplier and easier, while still looking great. Also, price wise, they are less expensive. I mean, that trap pack, $3.60! I'm picking up that.
However, once you get into it a bit, you should check out World Works Games for some good "set pieces" and some alternate tiles and designs. Also, they are doing stuff for the upcoming Pathfinder adventure path, so if you are going to run that, check it out. I'm not doing Pathfinder (I'm a 4E man myself), but I'm probably going to pick it up since I think it looks like a nice "set piece" dungeon I can re-purpose.