L Series by far, along with the sister mate M Series.
Sure the Model L had its growing pains, but thanks to certain dealers who weeded out those first L's and later the M's, the corp actually responded. I also know a certain CH who was instrumental in the shaping of this combine. By 1975, the L was doing good and even better, by 1976.
1977 put this combine back where it should be--a leader in harvest run business. At the time, only 3 of the 6 combine companies were really serious among CH's.
AGCO's big mistake, was not bringing the L4 back, under its own roof. By then, another, even larger conventional, like one with at least a 52 to 60 inch wide cylinder, should have been built. Still, as some have noted, the L's 48" cylinder was fully capable of keeping up with many 55" ones, due to the arrangement of the separator components and grain handling systems.