My centerpiece of all my work. I have the Top Turbo version with 1TB SSD internal HD and 16 GB of RAM. I run Logic and all other software synths. With Thunderbolt 2 I can connect my Apple 27" TB Cinema Displays and a big HD external screen with HDMI. Fast, powerful and easy to travel. With my Apollo Twin I have now all my studio with me. In my opinion don't use Yosemite! I still using Maverick and it works fine on everything I need.
Most companies make great computers, however, some computers are better at doing different things than other computers. I find that Macs are better for more artistic things, like photography, animation, editing, or just general art. And PCs, to be more for gaming and work. Now I'm not saying that PCs can't do artistic things, or Macs can't do gaming or work, but each brand has its own side on the spectrum of computers.