My experience with modulars is in fixing them. In theory a climate controlled area with workers who care would turn out a great product but the reality is that the workers are probably underpayed and couldn't care less. I am a general contractor and every one of the home's i build is far superior to a modular just because I care.
That being said, there are plenty of carpenters and general contractors who don't care and are just out to make a buck.
Ask around your area and you will find the names of the local contractors who will go out of their way to make sure you get more than what you are asking for. Try to find one who does start to finish. A lot of the time you will get a better product from someone who has more invested in the project.