If you want to be the best archer, you should go the heavy spellcasting route IMHO. With all the boost spells clerics (or wizards) have available, you will outshine the fighter pretty easily (that is, until someone dispels all the stuff). As a cleric you can also double as a healer, which seems like a great combination with someone who tries to stay away from melee anyways.
I personally prefer the arcane trickster route, tho, but that's just my personal preference, I just like rogue and wizard the most!
Greater Magic Weapon is almost inevitable to have against damage reduction and to turn a regular bow into a good magical weapon.
You can also get a simple +1 bow with multiple other enchantments and increase the enhancement bonus via this spell.
Persistent Divine Favor is also great.
Together, these two spells alone grant you a bonus of about your current character level to to hit and damage!
Elf domain is good as a cleric, because otherwise you don't have Cat's Grace, which greatly helps with the attack bonus, especially if empowered later. Time domain is another really good one. There is an elven god in the FRCS, that has both, BTW.
Fighter/Order of the Bow Initiate is the other obvious route, but will suffer from the lack of magical arrows, unless you throw in a few levels of arcane archer as well or got plenty money to spend on magical arrows.
Bye
Thanee