VirtualBox or VMware on Mac?

Both work fine. I use both on my Mac.

I don't have the newest VMware Fusion but I do have the newest Virtualbox. I personally think VB is better than Fusion and it is FREE.

I can share experience only of Parallels and Virtualbox; however, Virtualbox is a free open source. I use both of them to run Windows XP, Windows 7, Ubuntu, Fedora, and Gos. I personally prefer to run virtual environment instead of partitioning my hard drive and installing a non Apple operating system...that's just me. I have been using Apple over twenty years now and have always used a virtual environment since the mid nineties...a safer bet.

I've never tried Parallels. As for VMware Fusion, I'm using version 5 on 10.9 and I quite like it, except, something in the last few months has caused my Linux VMs X sessions to fail. I expect that Fusion 6 works like a charm. I'm kind of annoyed by the sense that I'll need a $70 upgrade to continue using a long-standing Linux VM. As such, I started using Virtual Box, since it's free. It's defintiely less refined and I've had some real issues passing in USB devices to my VMs (for low-level access anyway). VMware remains my preference, but I'm sad about the price. Ultimately, I'm likely to just suck up the gouge and keep on with VMware because I've got work to do aside from goof with VM settings. VirtualBox does work alright for most of my needs. So I guess for others the answer is a function of use cases and money. For basic uses or for people tight for cash, use VB.

The problem with getting into the main options like VM or Paralles is the annual cost of the upgrades. It is not a one time expense.

It is dissapointing they continually charge to stay current with the latest OS X.

I would recommend going with the open soure Virtual Box before you get sucked into the vortex.