Conclusions (subject to change - omitting unknown data)
Devcon 2 Ton is hardest - 23% harder than ETI Crystal Sheen, 2.4% harder than West Systems, and 3.6% harder than System 3
Devcon 2 Ton has best adhesion strength - 19% better than Crystal Sheen
System 3 has the highest tensile strength - 6.6% higher than West Systems
System 3 has the highest compressive strength - 18% higher than Devcon and 13% higher than West Systems
System 3 has a 10% higher flexural rating than West Systems
West Systems is 7.3% heavier than Devcon
System 3 has the longest working time, West Systems has the shortest
Crystal Sheen has the fastest full cure time - curing in 58% of the time required for Devcon
System 3 is the most free flowing, Devcon is the most viscous
Flex Coat is the only manufacturer to specify UV inhibition


Explanation of properties
http://www.matweb.com/reference/flexuralstrength.asp
http://www.matweb.com/reference/tensilestrength.asp
http://www.matweb.com/reference/shore-hardness.asp
http://xtronics.com/reference/viscosity.htm

Sources
http://www.systemthree.com/index_2.asp (registration required)
http://www.eti-usa.com/indust/epoxyind.htm
http://www.devcon.com/techinfo/179.pdf
http://www.westsystem.com/webpages/userinfo/moreinfo/properties.htm
(Manufacturer's data used per ASTM standard conditions as applicable)