I’d have to say Galadriel, but none of them really thrills me to be honest.
But if I had to choose I’d say Galadriel, Eowyn, Arwen in that order. I detested Liv Tyler’s performance in the movies so that hurts it for me.
I’d probably go with Eowyn, too, but Arwen isn’t so much a “decoration” as she is the symbol of Aragorn’s motivations. She doesn’t appear as a character, I think, because Tolkein just didn’t now how to write her (and realized it). But she remains the personal thing Aragorn fights for as opposed to the universal in the form of Gondor. It’s interesting that Tolkein described the univesal very well - we get a real sense of Rohan and Gondor as great civilizations - while the personal is hardly seen.
Galadriel. No one would pick a fight with me. Plus she is really hot and because she has been around so much, she knows stuff. Interesting stuff. 
On the other hand, you’d be picking fights with people all the time in defense of her honor. You wouldn’t even mean to; she wouldn’t ever ask you to. It would just happen, when you chanced to be in the company of the vulgar.
Definitely Eowyn. Her character has more depth and complexity than Arwen (although the films hyped up her conflict between choosing a human or elven life, there never seemed to be much doubt what her decision would be). Galadriel is more interesting than Arwen, but still a bit too aloof and distant for any real emotional interaction (from a human perspective, anyway).
Plus, Eowyn gets extra bad-ass bonus points for taking out the Witch-King of Angmar (albeit with some assistance).
Eowyn, for two main reasons. First is the badassitude others have mentioned, which comes with a serious helping of genuine courage: You just know that she was scared silly by the Witch-King, but she didn’t let that stop her.
Second, I try not to be racist, but let’s be frank, here: Relationships between elves and humans (or any other species with vastly different lifespans) have a way of going bad.
(and it doesn’t hurt matters any that Miranda Otto is hotter than Liv Tyler or Cate Blanchet)
Eowyn.
Two words: “Reverse Cowgirl”
Warning: Potential hijack ahead.
This touches on one thing that really bugged me about Jackson’s retelling, of which I am a great fan in general.
ARAGORN: I’m riddled with doubt.
ELROND: Arwen’s fate is bound up with the Ring. She’s dying.
ARAGORN: Watch out, Sauron. This time… it’s personal!
In Tolkien’s telling, the good guys put aside their personal fears and desires to do the right thing. That’s pretty much what made them the good guys. I’ve nothing against a good anything-for-love story," but that’s not what “The Lord of the Rings” was about, and Jackson and Co.'s attempt to shoehorn one in looked like just that.
Tolkien did write a tender tale of romance between Aragorn and Arwen that begins long before the war of the ring and ends long after, but he sensibly separated it from the primary narrative, and both stories are stronger for it.
I wouldn’t pick Galadriel. I couldn’t afford to buy her all those mirrors and phials.
Galadriel. Because she’s smart, and power is hot - and most important, because I’d be terrified not to.
Eowyn. She wouldn’t be all worried about heading off to The West and instead would be worried about heading off to The Best Western for some of that hot Rohan lovin’s.
Galadriel first because she’d know EXACTLY what I wanted as soon as I did… yow!
Eowyn next because I would yell “I’ll be boinked by no man!” and she’d be all like “I am NO man!” and rip off her clothes.
Then Arwen last because Liv Tyler… Dayam.
Arwen for sex, and if I had to have a lifelong relationship, Eowyn.
Galadriel is so far down the list she comes after the hobbits. Hobbit sex is ick. But she is before Wormtongue.
I really wish you had written “before Grima” rather than “before Wormtongue.”
Hey, don’t knock worm tongue until you’ve tried it! Has to be at least as good as moose head.
Anyhoo… of the three given options, it would have to be Eowyn. Galadriel is too freakin’ spooky, and Arwen is way too passive. Eowyn is full of spunk and could certainly screw your lights out. And then you could go shopping at the Gap of Rohan afterward.
But… if not limited to those three, I’d take Morwen (wife of Hurin). She was the original Goth chick, and we all know how freaky-crazy they can be!
Oh. I thought it was which one I’d want to be.. Which is Eowyn, obviously.
dangermom, the OP was purposefully ambiguous. “Which one would I like to be” is as valid a reading as “which would would I like to spend a no-strings-weekend with in Aspen” and “which one would I marry.”
Well, if it is “which one would I like to be,” then the answer is Arwen. Sometimes I just like to feel pretty.
And scream out in the throes of passion.
Sorry.
Appropriate smiley: 
My other half wants to know - what about Rosie???