I can give a bit of experience. Until 4 years ago, I had been exclusively a Windows developer. The only exposure to Mac that I had was cross-compiling applications on a G5, but never any direct development. 4 years ago I changed jobs, and am now completely Mac-centric at work. We’re developing a web-based health application with iOS and Android support.
That said, I can say, from our experience, Chrome and Firefox, on both Mac and PC, are the easiest to develop for, because they follow the standards to the letter. IE has their own take on the standards, so requires an extra bit of front end work, plus IE/Mac and IE/Win are DIFFERENT as well. Safari/Mac vs Safari/iOS also contain some different functionality.
To combat these kinds of differences, you can do several things. One, spend a giant amount of development (and continuing support) making sure that your application works the same across all platforms. This is the route we’re taking at work. Its a giant time sink, but you get the best kind of site out of it. OR, you can choose to support the lowest-common-denominator across all browsers. This is the easiest up-front, but you get the ‘worst’ functionality application. OR, you can do what t a lot of sites (including LSC) do. Support the majority of them for the lowest time investment, and have workarounds for the rest.
That being said, Mac vs PC is a religious or political question. 
