Modmagedanlanguage

Out of these options? Aether, easily. Honestly, I've only played it and Skyblock, and a modpack with Create, and out of those 3, it's a pretty easy pick.

Of all mods I've played, however? That's hard to say.
From a utilitarian POV, I tend to like minimap mods, item dictionary mods (see Too Many Items or Not Enough Items), Akashic Tome, inventory sorters, backpack mods and gravestone/death chest mods. There's a particular gravestone mod that stands out, but I can't recall its name. I think it had things you can achieve by dying? I felt like that softened the blow of death, some. And my current favourite minimap mod is Xaero's Minimap.
I have a bit of a soft spot for Thaumcraft, Witchery (and its successor Bewitchment) and The Twilight Forest, when it comes to magic mods. I know there's more I like, but I can't pick them off the top of my head.
For tech mods, I'll always like Buildcraft and Galacticraft. Been a long time since I've played either, though.

When it comes to modpacks, I've currently been playing some of Cottage Witch on ATLauncher, and I've been enjoying it a lot. It has quite a few mods that I have passing knowledge of from Youtube series I like, including the aforementioned Create, which, personally, seems a bit frustrating for my tastes. It also has Ars Noveau, which has been fun to learn. I've also been enjoying experimenting with the cooking mods available.

Thanks for posting this, it was fun to ramble on! Have a good day!