to be honest with a little practice, a hacksaw will be the most acurate tool, its bloody hard work though. A metal cutting bandsaw is probably best like this one
http://www.machinemart.co.uk/shop/pr...al-cutting-ban. These are great but never rely on the angle guage on the machine, always use a good quality protractor to set it up for each cut.(il have to give the credit for that tip to handyandy!)
I found the compound angles easiest to cut with a hacksaw because my mitre saw was too fidlly to set up. I drew all the cuts around the box section then put it in a vice so the cut lines were vertical and did it steady away
hope this helps