The term "modular" is a broad term that has changed over the years. Some would call a house that has partially assembled walls delivered to the site and assembled there a modular. My place was done that way, but, for all intents and purposes, might as well have been "stick built. The original owner and his wife wanted a new house on some land next to their current place back then. They contacted the company (Barden Homes) and were all set to sign on the line, when the
(a local school marm) decided she wanted the layout to be a mirror image of the initial plans, so they accommodated her. Once the house was finished, the refrigerator she ordered arrived and it was too large for the opening. They fixed that so she could keep her chosen refrigerator (ask any appliance dealer why most appliances are returned, and they will tell you it is because of improper fit). By then, all was good and They lived there for ~12 years. Another family bought the place and I bought it from them. Absolutely no problems with the house, which is now almost thirty years old, other than a poorly laid out flush drain for the water softener (fixed in less than an hour).
Whether you choose a "stick-built" or some form of pre-assembled house, what counts is who does the building, wiring, plumbing, and HVAC. If the person/company is reputable and skilled, all should be good for many years.