User blog comment:Deshiba/Mana Items./@comment-8919271-20140922143046/@comment-4022742-20140925103955

Athene's doesn't give flat mana, but it does give mana regeneration, which is definitely more profitable when you stay out longer without going back. Wit's End doesn't give AP but it does shred magic resistance from your target increasing all of your damage by a percentage that effectively gives the same effect as having more AP (read, either way your spells deal more damage).

This would hold true, if it wasn't for the Mana Font passive from chalice and athene's, for refference: "Increases your mana regeneration by 1% per 1% mana you are missing". So clearly mana regeneration DOES scale, both with items, base and regeneration per level.
 * "Mana scales, unlike mana regen."

With Archangel's, my version gives 7.5 more ap, while the AP gained from Lich goes down by 20, loosing out on 12.5 AP, overall a nerf to people that don't get Archangel's and a nerf to people that do. The 250 mana gives Kassadin 5+15 (Max Stacks) damage on Rift Walk while he looses 40 damage overall. Since you were talking assassins in your original comment I limited my logic to that. Even so he gains a total of 35 damage extra while he looses 41 damage overall. The loss of 20 AP is more damaging to their damage on RQWE then the 250 mana is beneficial. However, like I allready mentioned, the 50 MR should be lowered to be in line with Athene's and Wit's, 25 MR should not be a problem.
 * "Mana translates into AP from archangel's and, sometimes, into direct damage - like Kassa's R and Ryze's QWE."