Is surgery or HT/RT best for minimising ED & incontinence

It's a risk for both treatments, but current radiotherapy is thought to have a lower risk of impact than surgery.

With surgery, the location of the cancer and your anatomy can change the risk, as can the expertise of the surgeon. Cancer at the rear of the prostate near the neurovascular bundle (the most common position) increases the risk of ED. Cancer in the apex of the prostate also increases the chance of incontinence. Having a short membranous urethra (the part which goes through the pelvic floor/external urinary sphincter) also increases the chance of incontinence. These are all things your surgeon should be able to advise you on based on your scans. Retzius Sparing surgery (performed by a small number of surgeons) gives a faster return of continence after the operation (often immediate), but a year later, it makes no difference in continence as the standard (retropubic) prostatectomy patients have caught up (mostly by 6 months).

With radiotherapy, I'm not sure there are as many identifiable factors which govern your risk of ED or incontinence. The urinary incontinence risk is much lower (but not zero), but there's a very small risk of rectal incontinence (probably even less over the last 6 years due to much more accurate aiming and masking). Unlike surgery were ED is instant in nearly everyone and you hope it recovers over the following months or years, radiotherapy rarely causes ED immediately, but can cause gradual onset over the next 2 years. If you reach 2 years after RT and erectile function is still OK, then you dodged that bullet as onset of ED then reverts to being at the same rate as men of the same age who never had prostate cancer.

It might also be worth pondering the fact that techniques have been and still are improving for both surgery and radiation.

This could be something to weigh in the balance in favour of AS if you have the option of waiting and are still considering the various pros and cons - in the words of Dr Scholz "would you rather be treated with 2024 technology or 2028 technology ?