Either Parallels or Fusion work well. I have used them both. The last time, I used fusion with Windows XP for old games and it was a very good experience.
It is important to be aware however that while many titles, particularly older ones that are not as demanding of the hardware and utilize DirectX 9.0c or earlier are likely to run great, you will encounter titles that simply are not compatible within a virtual machine environment on any version of Windows from XP to 10. I ran a lot of different games and many worked well but sometimes I'd run into something that ran at a glacial pace despite being old or would not start or whatever while it would run flawlessly in bootcamp. So I knew it was not a Windows issue. It had something to do with the GPU functionality of the VM software in all likelihood.
I bring that up just so that you understand you are not going to get 100% compatibility even with older games. That said, I found it quite worthwhile where so many titles ran very well.
As far as performance goes, the more powerful your Mac is the better off you will be. You did not mention the specs of your Mac unless I missed it so I cannot give you any idea what to expect there. My experiences were on a 27" mid-2011 iMac with a 6970m GPU, 8 GB RAM and I forget the CPU, probably a 3.2 and it was an i5. For the past two years it has been a late-2013 27" iMac with a Nvidia 775m GPU, 8 GB RAM and 3.4 i5 CPU.
I allowed 4 gigs of RAM to XP although it can't use all of that because I was not running anything else anyway and I could not be bothered looking up the exact amount of addressable space it could handle which I know is somewhere between 3 and 4 gigs. Yep. I am that lazy. I configured it with 2 cores as that was plenty for anything that would run well enough to suit me on it.
For newer titles I personally consider it to be more comprise than is acceptable to me so I'd reboot into Windows for those. While it seems to not be problematic for some, I do not advise using their tech to access the Windows bootcamp install directly from within OS X which they push as a great feature. What I found in doing that was that Windows would detect the hardware change and want to validate itself again. When I consulted support about this they were aware of the issue and blamed Microsoft for the validation problem. When I called Microsoft and explained I am simply running one single licensed installation of Windows on one single computer, the only one I own, they informed that they do not support this scenario and that it is necessary to purchase an additional license if you wish to run Windows in both a virtual machine and installed on the hard disk of the same computer. Yes, I find that outrageous too but I am not making this up. I did call them. That was their response. So, Parallels won't take responsibility for this promoted feature not working very well and Microsoft requires paying for Windows twice or too bad about you.
Somebody may come along and claim well it works fine for me. That's great but it does not change what I saw and experienced here nor the responses I got directly from both companies involved. YMMV I guess.
In summary, I consider this stuff a good tool for accessing more games without rebooting but it isn't perfect so just be aware of that. As for the free Virtualbox, don't waste your time, not for gaming anyway. It's not up to snuff for that, not nearly.
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The bigger question is: Will Windows XP install on a current Mac? I would say you would have to at least use Windows 7.
Why is that a bigger question? It will install in a virtual machine with either Parallels or Fusion last I knew. However, I was not using the most current Parallels so confirming it still supports XP would be a good idea. Fusion 8 which as far as I know hasn't seen an upgrade lately, did support XP. I used it with that version. I am guessing maybe you are thinking of bootcamp where it isn't supported anymore?
