I prefer self-enchanted bows. So start with a very powerful base bow. This means an unchanted daedric, perfect amber or perfect madness (depending on the look you like), then enchant it with a grand soul gem to suit your playstyle. Consider adding a biref soul trap effect to the bow and carrying Azura's Star to keep it charged.
The unique bow found in one of the Oblvion worlds looks like a daedric, but is a more powerful base bow. I prefer my own enchantments over the slightly higher base damage. My problem with that bow is that the enchantments are just 'ok' (for my purposes), it has too few charges and lacks soul trap. Many people like that bow though, so try it out and see what you think.
Remember of course, that any bow goes better with sneak and poison.