If you are cutting a lot of wood, favor a machine that has large prefilters in terms of surface area. Wood generates much more dust than gas: 90% dust versus 10% gas. In this case, favor a system that has a large prefilter in terms of surface area. Also look for machines that have rigid metal filters with good seals between them. Under heavy dust load and high pressure from the vacuum blowers, filters encased in flexible materials, such as thin cardboard, may warm and leak around the seals. The dust bypass through the leaks leads to premature consumption of HEPA and gas filters.