What kind of belt for router table?

I am getting things sorted out to build a 4' x 4' cnc router table
(maybe run some oxy/fuel cutting too) when I go to the Mcmaster Carr
web site and type in drive belt I get back 1,100 choices! which type
of material is best suited for so I get no backlash in the belt/drive
gear teeth mesh and can withstand being tight without stretching.
some of the choices I see are pure urethane or stainless steel with a
nylon coating and rubber. I could not find any kevlar belts there
though. thanks.