Self crafted and self enchanted weapons are the best weapons in this game. My bow has 350+ dm plus the sneak bonus x3 can one hit anything.
Well I don't think I'm doing quite that much damage, but yea. Most of the rare/special bows are lame... The only one that seems close to worthwhile is the nightingales bow like what has been said already. As I would have loved to have been able to get that enchantment. Other then that a self crafted bow is the best route.
As far as the Drainspell bow... That was a big disappointment to me. Absorb magica... Really! One of the coolest looking bows, and you put the most worthless enchantment on it for an archer. And if it was in thought that it was support to be for a Mage then that was a lame idea. How are you support to cast spells with it? Lol worthless. Or maybe it was ment to battle mages... Nope there dead way before I could effectively drain there entire mana pool.
There is also another rare bow that sports the almighty absorb Magica too!
Anyway good bow make ups would be anything like...
Firiey soul trap- good for getting souls with a little umfff
Paralyze- alright if it works
Absorb stamina- awesome enchantment for bows!
And I'm sure there are some others that work for various set ups or builds.