I have installed Mavericks on my PC, now I want to install Ubuntu 14.04 but I'm not sure which file should I download: 64-bit or 64-bit mac.

I have installed Mavericks on my PC, now I want to install Ubuntu 14.04 but I'm not sure which file should I download: 64-bit or 64-bit mac.

Macs can't boot multi-catalog CD images, that's why there's a separate 64-bit Mac ISO.
If you're running on an actual Mac made by Apple (not a Hackintosh), grab the 64-bit Mac version.
Most Macs with Intel processors will work with either 64-bit or Mac images. If the 64-bit image doesn't work, try the Mac image. In case of Macbook, you prefer to use 64-bit Mac.