I already got my chance to reply to this question on that "other site", but for those who don't go there....
My #1 favorite developement was without a doubt the "DX" series, (better known as 100 series utilities and 1000 series bigger row crops) They were simple to work on, stone reliable, economic to operate, and at the low end of the price spectrum compared to their competition. The improved "Ferguson System" draft control and position control was the best in the industry at that time. It's still a tough act to beat all these years later. A few individual models excelled. The 1100, 165, and 135 models were the stars of the show. The 135 being a true ledgend. Their star qualities still shine more than 40 years after their introduction as they STILL bring quite a nice price, and with the majority of them still in the field working every day. The 1971 MF 150 pictured in my avatar is, IMHO, one of the finest tractors ever built.
Also, the model 300 combine was a pioneer of sorts. In the late 1950's and on through the mid 60's, Massey Ferguson led the industry in combine sales. They sold more combines than Deere, IH, Gleaner (AC), Ford, Case, Oliver, ect. The model 300 was the reason why. It had a long list of "first's" that are now considered standard features on todays combines. Massey Harris was a leader in self propelled combine design. After the merger, Massey Ferguson took the ball and ran with it. Massey combines still have a great reputation to this day.
As far as "flops", the mid-60's saw "Pressure Control" being touted as "the way" to pull drawn type implements to give the same advantages as draft control and mounted implements. It simply never caught on.
Another bomb was the MF25/MF130. A small French built companion to the MF35/MF135, it had poor brakes, not enough power, terrible steering components, and never got the parts support of the rest of the Massey utilities of that era. For just a few bucks more than the cost of a 130, you could buy what was quite possibly the best tractor value EVER, the MF135.