I used to use qemu on linux,
but it seems not functioning well on osx,
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.If this question can be reworded to fit the rules in the help center, please edit the question.
If you are looking to game on Mac - use Parallels. Hands down it has the fastest 3D-acceleration virtualization on Mac.
If you need to run productivity apps mainly, then go with VMWare Fusion for its outstanding support and configuration tool, as well as superior OpenGL and productivity benchmarks.
If you would prefer free, then go with Oracle VirtualBox.
For a comprehensive review, you can read this article on Ars Technica.
I personally prefer VMWare, as it has a long history of outstanding virtualization products, and productivity performance is more important to me.
VirtualBox is currently the best free one. Commercially, in general VMWare has slightly better guest compatibility whereas Parallels is slightly faster — but you should probably ask a search engine about the specific hypervisor and guest OS you want to use, to see if there are any known issues.