GW models are generally top notch, and the latest models are technically very impressive. They are generally very well engineered. Because of their popularity GW models tend to be seen as the 'default standard' which I think is hard on smaller, newer manufacturers. I recently put together some Conquest minis, and while they were good, the building experience was inferior compared to that of Gw's, what with the engineering and clear instructions they generally offer.
I have the Song of Ice and Fire starter set, and I think those single piece minis are excellent.
I don't like GW's trend in making minis taller, bigger, thinner and easier to break. So I won't be going down the Lumineth route.
The 3d printing STLs I've seen are far inferior to GWs level of detail, but that is a medium that's constantly developing and improving.