Neesy if you'll give me a list of what you wanna do with it and your true technical knowledge level, I'd more than happy to be a free consultant for you. I've been using computers at expert user level since 1980 and worked in IT since the 1990's. I can get more specific then and send you a link to a configured model.
For the most part, I would suggest a MacBook Pro for a super snappy, pretty much error free experience. Of course they are pricey. But I can tell you that we buy each kid a new one for graduation and so far the 3 we bought have been rock solid. I've never had to once help them fix anything. They just work. The graphics, web browsing and music experience on Mac is the best.
I make my living off Windows and have for many years now. Windows 10 is good, but like Ghost said, lots of RAM and also an upgraded video card. I wouldn't go below 8GBs of RAM and also the higher frequency chips if possible. Again, depends on what you're doing with it. I am typing from a Dell XPS right now. I still have Windows 7 Ultimate, but that's because I am a grump. My son has a Dell gaming PC that runs Windows 10 and it hasn't really had any issues in the year he's had it. I have a few expired Dell certifications, mostly server stuff, but the point is I've worked with Dell machines since they were a startup. I was in Oklahoma relatively close to their HQ then and so was exposed early. They used to be AMAZING machines. Now, I'd say the upper level ones are still pretty good, but the lower down the ladder you go, expect to be more disappointed in its life and performance. The span from zero of the initial bathtub curve of failure is wider for the lower end models than the high end. Essentially more initial failure in their cheapo depot models now.
HP has lost a lot of its mojo, but I've heard some good things about their newer laptops. Desktops are a toss up. I'd go Dell over them. As referenced, Lenovo makes some really quality stuff. But again, don't cheap out.
In the "biz" we call these brand name PCs "peanut computers", because they come in a box filled with Styrofoam peanuts. I think you get the basic idea though. If you're going to get a Windows machine or PC, then don't go low end. Middle grade is Ok if you're trying to save some cash or don't need a big performer. Normally you will get lucky with a mid grade and get 4-5 years out of it. The thing with PCs is that since the operating system is so flexible itself, the configuration of the hardware you choose is also flexible. With Mac, they come pre-packaged in a limited number of configs that address most everything a person would want at each threshold.
Another option not mentioned is to find a reputable local PC shop and have them build one to spec for you. Normally they will have pre-built stock models you can pick or customize, or they will build one ground up for you. You can typically get a really quality machine for less. If you're really feeling froggy, you can also buy all the parts and software and build it yourself. You can usually build a high end PC for half the cost or less of buying one. Of course you have to know what you're doing...
If I can help further, please let me know.
Please - no comments from the Peanut Gallery 
