IMO both are better meshes would be a good option, you should tend to use meshes for more complexed models that could be made in a software, you should use meshes for more detailed models, such as for making (swords - guns - cars ect). From what I heard meshes take a while to load in, consider using a variety of both options including parts and meshes.
I would suggest using meshes for more higher details, however, both options are useful in all sorts of things use parts for more simple methods and meshes when they are needed in your case. There are a few similar threads to your question regarding the use of meshes vs parts: