Hi,
Dan from CCP writes about VXC here:
http://canadiancouchpotato.com/2014/07/10/under-the-hood-vanguard-ftse-all-world-ex-canada-vxc/As he mentions, this will lose the withholding tax, but you get the convinence of a merged US/international fund as well as not needing currency conversion.
In terms of the "best" place to hold it - it's always better to have funds in RRSP/TFSA versus taxable. In this case it doesn't matter much between RRSP/TFSA since this isn't a US registered fund (which gives a slight advantage to RRSP).
Since you are using the general advice of putting bonds in taxable, I would suggest the simple model of:
Bonds in RRSP until full. If full, then TFSA.
Next VXC. RRSP if room left, then TFSA, then unregistered.
Finally, VCN. RRSP if any room left, then TFSA, then unregistered.
The main point is it is better to have VCN in unregistered compared to VXC - because of the much mroe favorable dividend treatment. It's always better to use RRSP/TFSA if available though.
Hope this helps.