Best computer to get for video editing?

I have a wedding video business and I also make a lot of videos besides weddings. I currently use a year old Lenovo laptop, it's called the Lenovo ideapad. It is great but it gets slower and slower and lots of times it won't save my videos. I edit with sony Vegas. I'm looking to upgrade to possibly a desktop or a really great laptop that can handle the work that I do. What kind of computer is good? Also, should I get a mac so that I can use Final Cut Pro? Or should I stick with windows and sony Vegas? Any help is appreciated thanks