50 hp is plenty. You didn't say if the prices included the loader and hay handling equipment, such as a grapple or spear. It might be useful to compare them as equipped for the job at hand. You might even include the mower if you know you'll get one.
You want a stable tractor with powerful hydraulics. Either should be OK. Front wheel assist would be helpful in many cases unless you need extreme short turning. The shuttle gear is very handy when backing and maneuvering.
For tractors of this size, I assume you are looking at category 2 three-point-lift. Most 3 points on tractors like this can be converted to cat 1 if you need to. You'll have an internal lift cylinder.
Look at the hydraulics. You may want at least one and possibly two external hydraulic valves in addition to the ones used to operate the loader. That way, you can have the loader on and functioning and still operate something without unhooking the loader to use it's hydraulic connections. The loader may get hydraulics directly from the pump or may connect to the external valves. The loader boom needs cylinders as does the bucket to tilt and some have a third set to operate a grapple or other accessory. You can see how it is possible to run out of hydraulics. Look at the controls - do you have one or two and are you happy with that? Some use a joy stick that works front-back for the boom and sideways for the bucket, for example.
For the mower, you'll have either 540 or 1000 rpm power take off. At 50 hp, 540 is enough but keep in mind that as you get equipment that takes more horsepower you might prefer a 1000 rpm system because it can handle more torque.. In any event, your tractor and equipment have to be the same. Some tractors have dual PTO systems or ways to change from one to the other, but it's something to check out.
As you likely know, you can buy all manner of used tractors with loaders, PTO and a three-point-hitch for well under $10,000.
