Given the mix of mowing / disk work and loader work, this one is a tough call.
For me, if price were no object, and I could get the tractor I want with HST or CVT, I would take either of those over gear (including hydraulic shuttle). However, given that an HST costs more with the same engine and actually requires a bigger engine compared to hydraulic shuttle to get the same pulling performance, the value argument and "good enough" convenience of the hydraulic shuttle is what I went with.
Given that you said you just want "the best". And since you said this is your last tractor. And since none of us know what life will throw at us in terms of physical injuries / issues. For you, I suggest you get the biggest engine you can get with the HST tranny.
Here's the catch. When you price it out, you will find that you could get a bigger tractor with a hydraulic shuttle for the same price. More weight, bigger engine, stronger loader etc. This is where I always get hung up and so far have always valued bigger and stronger over the HST tranny.