I use Linux on my home desktop and my work desktop but I also keep a Windows install on my work machine when I need to test Windows things there. On Windows, I haven't found a better Git GUI than fork.dev. It's not open-source but it is what one of my favorite creators calls "organic software": Ukrainian husband and wife duo that warms my heart. The evaluation period is unlimited without nags. I've found it to be the perfect Git teaching tool and the best merge conflict resolver I've ever seen.