Watchful waiting and active surveillance are slightly different. You would almost certainly be on AS with the objective of curing the problem if it starts to advance.
Unlike pallance, though I respect his opinion, I would be inclined to AS with your disease. These cancer treatments are not pleasant if you can avoid them or delay them then that's what I would do.
I think you need three things in place if AS is to work for you:
1. The onco says it's appropriate for you.
2. You have a personality type where you won't suffer anxiety with this approach.
3. You trust the hospital to do the psa tests, biopsies etc. and not forget to look at your file.
I think the best thing about AS is it has no side effects, if you decide at a later point to change your mind and have treatment you can. If you go down the radical treatment route, you can't change your mind once it's done.