There isn't really a "best" Linux distribution. Try them for yourself, and stick with whichever one you like the most.
The more popular distributions are Ubuntu, Mint (an Ubuntu derivative), Arch (please don't try this one as your first distro), and Fedora. Of those four I like Arch the most, but that's because I know how Linux "ticks", so to speak. Ubuntu, Mint, and Fedora all have graphical installs. Arch is command line, and while it isn't a very difficult install, it's daunting if you have no Linux experience, and especially no Linux command line experience.
If you're looking for a good first distro, I would tend to recommend Fedora. It's more up to date than Ubuntu and Mint, while still being user friendly and stable. I've also seen Elementary OS thrown around, and that might be a solid first choice given that Elementary is an Ubuntu derivative, you're currently using a Macintosh according to your sig, and Elementary's desktop environment is very similar to Mac.
Really, though, the distro you use it up to you. Try the ones that intrigue you, and whichever one you like, go with that one. The reason so many distros exist is because people didn't see a distro that fit for them, so they made their own. Linux isn't about having a "best" distro, it's about having the best distro for your use case.