My Suggestion.
I suggest this system because I know it works. Given the maturity and community spirit of Genesis Claymores, I can't see how it would fail.
Essentially my suggestion is a need/greed affair, with a few tweeks here and there. Priority is to main spec, which would be defined as the spec you normally raid with (so for example if you are usually dps but go healer for a raid, your main spec is still dps). After main spec rolls are off spec rolls, and if no one wants the item for either it's given to an enchanter and put into the guild bank. Other than the basic archetype stat weights, all rolls are equal.
The beauty of this system is the ease of use - theres no note taking, no addons or spreadsheets needed, no work for the officers/raidleaders other than simple masterlooting. It does depend on everyone being mature enough to realise that no they might not be guaranteed an item every run, but the guild as a whole will become stronger. It also benefits from people having the knowledge and inclination to pass on certain items that would benefit another player more than themselves, the raid is more important than the individual, but then every system conceived benefits from that. It also means that loot is dealt with quickly, I've seen one dkp system take 45 mins to decide 1 item, and on more than one occasion. Loot dealt with quickly, means more time in a raid to do other bosses, means more loot, means a stronger raid.
Hope this all makes sense, if not I shall happily clarify.