I have Windows 8.1 it's fast and good for me but I don't know it's right to upgrade to 10
Why would you want to upgrade to a preview buggy alpha/beta release? you should at least wait for next year for the consumer preview, if you want to try it, but I think it's risky and not worth it.
Windows 10 has nice new things, but if you are on Windows 8.1, then there is no reason to force your computer and yourself to lose information, to reinstall Windows if it stops working at all.
You could use a virtual machine and test it that way, it's nice, but not worth it the effort of installing it and getting many bugs that comes with it.
I think for the moment, it's easier to wait for a consumer preview or even RTM and only install add-ons to Windows 8.1, you know, to get shadows and start menu, and windowed apps, and also to get multi desktop support. because this windows 10 preview is basically that.