Couple of workflows and questions:
What flavor of XDCAM? SD, HD, or EX?
Are you doing alot of effects work, color timing, etc. in your MC timeline? Is your machine older? If so, DNxHD is better.
Is this a reality show or a doc? Then it may be best to do the XDCAM proxy video & high res audio workflow, then switch to high res video after the edit.
It should be noted that anything AMA has limitations in terms of track count and RT performance. Although the XDCAM workflow via AMA is more robust than the Quicktime AMA workflow, there are still a few hiccups to be aware of.
If you have the time, I always recommend going to a DNxHD flavor over a camera native.
~Michael
.: michael kammes mpse
.: senior applications editor . post workflow consultant
.: audio specialist . act fcp . acsr
.: michaelkammes.com