Mechanical schematic design software

I don't have any experience with the type of software you are probably looking for. My experience is mainly with 3D mechanical design software. I am guessing you are looking more for building layout/duct/piping type software? I think some of the pros on here have better ideas than I do. Some of this decision depends on how much money you want to spend. The more "output" you want the more money, typically. The standard in building design and layout these days is Revit, but that is generally only used by larger design/engineering firms that have the money ($$$). My company actually outputs all our units in Revit to insert into building layouts. Wish I could be of more help, hopefully one of the pros has some suggestions. I would start with a list of what you want it to do, you really need to know that to be able to find any software.