What would be the fastest way to do it?
Should I do Elite AoM then Ultimate or just Ulti and grind mobs?
Do the Malmouth Resistances quests on all difficulties (along with other quests) to get Revered, then buy those Clarity potions (+100% experience for an hour) and use them while turning quests in/grinding mobs. Elite/Ultimate doesn’t matter as long as enemies are at or above your level.
Elite AoM will give good experience, and get your rep building for Ultimate.
I just did Ultimate AoM straight way first time I played with level 85 character in AoM. Grinding reputation is not that hard really, maybe 1 or 2 extra runs with bounties. I don’t think going back to Elite is worth it, unless your build sucks.
Unless you have a top end level 85 build, you will likely struggle as so many did at the start. Suck, or rather, less than ideal builds, will make it difficult in AoM. You can always try Ultimate, but most people struggle without being level 94, when going into ultimate AoM.
I start in elite, the rep grind is much easier if you rush it before starting ultimate.
You also tend to get wrecked in ultimate wearing pre-expansion gear if you’re not careful.
I did elite AOM and worked on getting Kriegs set. Took awhile but I finally got it.