Honestly, I'd say it's personal preference. I'm just shy of level 60 and still using my first legendary bow (I also know a lore-master who, at level cap, still uses her first legendary staff). If you can find one with the legacies you like and really advance it, then I wouldn't worry about what's "best". That's the beauty of having legacies on these weapons, they allow for all different sorts of play styles and preferences.
If you are lvl 65, I would imagine you would want a lvl 65 second age bow. IMO, the particular legacies you have on it are not that important, as long as it has some legacies on it you find useful. Of course, I am not one of those perfectionists that constantly grind out relics to get to that "ultimate" bow with 6 starting legacies all at tier 6, critical multiplier, induction power cost, etc. etc.
A level 65 second age is the best. For my hunter, I require that his bow have Barbed Arrow Bleed Damage and either Induction or Focus Bow Critical Damage. Induction/Focus power cost is nice, so is strength quick shot slow, and quick shot critical rating, but really, it is not hard to get a decent hunter bow.