I've tried a number of companion mods and Vilja is by far my favorite. HOD (Heart of the Dead), Stoker Wolff, and Ruined-Tail, Arren/Baddy, and a custom companion I made for myself have all had a place in my game.
Vilja's got lots of personality while not being particularly demanding; that's a great combination. Vilja's the most lore friendly of the bunch and I love listening to Emma's voice acting. The big theme for my preferred companions is personality.
Pretty much everything I want will be in the new version of Vilja (coming soon), but that's because I've been helping create it. Arren/Baddy has some demanding quests attached to trigger on level which is annoying if you level up too quickly. I also like that Vilja's quests are directly combat related.
I think all companions should come with a way to let the player choose in-game if the companion is essential or not.
Voice acting is extremely important for a real companion in my opinion but it's not vital. The character doesn't have to say much but there should be some sound because Oblivion characters talk. (My personal companion couldn't do much more than "yes?" and "um" but at least there was some sense of interaction.)
Quests to get a companion can be annoying. Little quests with a companion are good though. Vilja is a perfectly usable companion from the time you meet her but you get extra features over time if you help her and interact with her. That's the "companion with quests" model instead of the "quest with companion" model.
Hunger/sleep/thirst needs would be a negative from my perspective, but hunger/sleep/thirst desires are good. Vilja will comment if you stay up too late and will ask for food and drink. You are aren't penalized for ignoring her requests but you can rewarded for helping her. (And if you hang out in a city there's a chance she'll decide to run off to the local tavern to have a drink.)
I'm not sure I understand the difference between get-and-go and realistic/emotional/unique. There's no reason you can't have both in my way of looking at things. Vilja and Arren/Baddy both fit into that mold fairly well. You pick them up, start traveling together, but then get to know them better over time.
[*]Are there any elements you would like to see in said mod that aren't there? - Most of my wishes are being worked on, but not sure if different wardrobes will be as expanded/functional as I would like, maybe one day but its not as important as the rest of Viljas qualities.
No, you're not going to get everything you want. Sorry. Emma doesn't want OBSE dependencies and multiple wardrobes really requires that. I haven't wanted to spend the time creating that feature when there were so many more interesting things (by my definition of interesting) that I could do. She will have a swimming outfit and you'll be able to control what she wears when sleeping, but that's it in the next version.
That does raise the issue of inventory access and control. The new Vilja will have three storage areas in addition to her main inventory, one holds her pyjamas but the other two are purely so that the player can have her carry things without using them.
Another companion feature I've missed in Oblivion is encumbrance. Every companion is able to carry an infinite amount of stuff. In the new version of Vilja you'll have the option to have her follow the same encumbrance restrictions as the player.
What I'm really looking for in a new companion is someone like the upcoming version of Vilja in the technical details but with a different background and personality but still within the Elder Scrolls lore. Someone that Vilja can have a conversation or even argument with would be nice.
A non-combat focused companion is also welcome. How about a cowardly companion that runs and hides at the first sign of conflict?