Tough to tell the age of the Ariens. If it has a short chute with 9 inches from the base toothed ring to the hood nut then it’s probably and early to mid 80’s. If it’s about 12 inches then it’s probably a mid to late 80’s machine.
If it’s got a rounded bull nose gearbox then it could be the early version. If it’s got a somewhat rectangle shaped gearbox that is stoodup on end then it’s probably mid to later 80’s.
The Simplicity seems to be a generation newer with the given the chute style and remote control and in the 90’s, possibly 91-98.
Overall age is not so important as condition. The Ariens has differential. The Simplicity has pin locking. Both are great machines. The Simplicity will probably toss a bit further than the Ariens. The Ariens probably a little easier to handle. I have a Simplicity 870E and it’s ok but a little sloppy in the tractor section.
I’d flip up both machine and check out the internals. Move the wheels and see how much slop there is in there. Shake the internal shafts and parts to check the slop and wear.
The engine compression would be one of the big concerns. Do a leak-down test on both if you have a tester ($30 and worth the cost). Check for rust in the Briggs tank. It probably does not have a line filter.
