Windows 8.1 is an update, not an upgrade. What that means is you can go ahead and buy vanilla Windows 8 SKUs, you will get the 8.1 update free.
Worth trying the Windows 8.1 Preview, but I have found it has some bugs, as should be expected of unfinished preview/beta software. Also, remember, you will lose all your installed apps on both metro and desktop when 8.1 final is released. So unless you feel adventurous the best option is to buy Windows 8, it will be updated to 8.1 come October 18th.
Worth trying the Windows 8.1 Preview, but I have found it has some bugs, as should be expected of unfinished preview/beta software. Also, remember, you will lose all your installed apps on both metro and desktop when 8.1 final is released. So unless you feel adventurous the best option is to buy Windows 8, it will be updated to 8.1 come October 18th.