I can't really recommend a "best" Windows system. I'm sure there's others here more hardware savvy than I but as long as you stay away from the entry-level spec systems and components, you'll end up with a machine capable of running Win 10 smoothly. I've got 10 on three machines in this house, one of which is a mildly upgraded POS $300 Wal-Mart Acer laptop and it works great. There are a few suggestions I would make in regards to performance:
1) NEVER install Flash or Java. They are the largest security risks you can have on your computer and they try very hard to hose your system with constantly running background processes and by installing extra and unwanted software during updates, further hurting your computer's performance. If you absolutely have to have Flash, use Google Chrome. It's built into the browser so it is patched quickly and doesn't try to install extra crap on your computer.
2) Be careful what you do install. Windows performance degrades over time primarily because of it's registry-based system and the fact that any software is allowed to stick their fingers in it. Even after you uninstall something, without extra forensic work, the uninstalled software usually leaves behind elements that gum up the works, slowing things down a tiny bit at a time at best or even causing errors and crashes when things can't be found at worst.
3) Take care of your investment! Every once in a while, do a little bit of preventative maintenance. Check for malware with MalwareBytes
(free), get rid of orphaned and unneeded files and clean your registry with CCleaner
(also free) and let the built in Windows Defender(the free trifecta!) do an automated scan once a day to check for viruses or malware. To keep it from ever showing up, never click on links in emails from people you don't recognize or that don't make sense, don't open zip files, run programs or click "OK" any time your system asks you if you're sure you want to allow something to happen if you didn't expect it to and always run an ad blocker (malware is often passed via the ad networks that are serving you the advertisements).
It's pretty popular for people to bag on Windows of any version but I've run them all successfully and although I choose to run linux personally, my whole family runs various versions of Windows daily with no issue at all(We have all versions from XP to 10 running in the house right now). Any version is capable of working well with proper setup and a little common sense.