ElitistBody841 you have done a good job of discussing the bonuses you get with each of the 3 alliances but these bonuses are just one of several issues to consider when deciding which alliance to join.
Other considerations might include:-
How EP rich you are:
Many Imhotep players join this alliance because of it's improved AP to EP reward ratio.
If you are flush with EP then the higher bonus with Imhotep is of little significance.
Which of the available alliance equipments appeal to you ?
I suspect many players favour Delian on account of their excellent equipments.
eg Delian Adept's Wheels which add 28.7% damage to siege units with no cost increase.
Which alliance are your pals in ?
If you want to do co op alliance quests with your pals this may well be the deciding issue.
Which of the bonus's complement your play style best?
A player that likes multiple military production buildings so they are able get out a large army very quickly may well find the cheaper buildings bonus very appealing. ( ps - This doesn't only benefit the turtlers ! )
One strategy might be to initially join Imhotep and enjoy the extra EP bonus and continue with them until you've made the various EP purchases you want. At a later time if & when you've more EP than you know what to do with switch to a different alliance.
Just bear in mind your decision isn't a "set in stone" one. If you wait until the 24hr , 7 day & 30 day wars end and have got all your AP converted to EP, you can leave your current alliance and join a different one & you will loose nothing** but your rank.
Rank can usually be got back again fairly quickly so this is no big deal either.
** This does assume that you've not spent a fortune on specific alliance equipments.
You can only use equipments from your current alliance so specific alliance equipments may need to be replaced if you switch alliance.