The two combines are basically the same except for the cab and the hydraulics. 2188 will have better brakes, concave control(in cab),bigger cab, better spreading(2188 should have chaff spreader, 1688 could have chaff spreader but probably has straw spreader. Chaff spreader is a plus). Determine whether either combine has a field tracker or not. Personally I would prefer a 2188. Just my .02 worth.