Sean, many of us here have been in the same situation and had to make their choice. There isn't a "right" answer, all the treatments have similar success rates, but there are obviously things that might influence your decision.
Your age is one, someone in their fifties is inevitably more worried about side effects that appear decades later than someone in their eighties. However if your hospital has the latest generation of radiotherapy machines the effects on surrounding tissues should be minimised.
As you say, surgery does have the advantage that radiotherapy is still an option should there be a recurrence, That happened with me - but of course I don't know whether I would have done better with radio first time. The other benefit though is that after surgery PSA should be zero, so even a small rise can be detected and acted on.
When I was first diagnosed I thought brachytherapy sounded a good option - but then it turned out my prostate was too large (and I would have had to travel a long way to access it anyway).
There is a lot of experience of the different treatments here on this forum, but all any of us can do is describe our own experiences, we can't know how the same treatment will work for you. You just have to go with what you are happy with.