A bit of a tough call!! Both your options are well-regarded tractors in the 150-165 hp range, with features suitable for haymaking. The Deere 6R series is known for its robust build, advanced technology and a well-established dealer network with strong parts and service support. The Massey 7S series on the other hand, is often cited for its fuel efficiency, which can lead to lower operational costs over time.
The upfront price of the Massey may be lower, but the long-term cost to run can be influenced by multiple factors like fuel costs, maintenance schedules, parts availability, and resale value.. these can all vary depending on your specific location and usage. You might find that the total cost over a few years, once you factor in servicing and any little repairs, evens out pretty quick.
Maybe try to get more info and compare detailed quotes, including service contracts and warranties from both dealers.