Okay, hate to break the argument, but just throwing my 2 cents (yeah, i know nobody is going to read this but I like writing this stuff):
Anyway, I have to break this down into subcategories, because I'm very, very split.
Aesthetics: Empire by far. I've always liked the gray-scale look of the Imperial military, and the symmetry and uniformity of everything. I also liked the massiveness of capital ships compared to the tiny fighters they had... the contrast in sizes just gave a fierce look. Having small fighters to accentuate the size of capital ships definitely would increase the fear factor into the enemy. And... as much as I like heroism... I also like the idea of a uniform, nameless-faceless and numberless army. Talk about intimidation! That, and in my opinion, the best looking ships in any sci-fi have to be those produced by the Empire.
Playstyle: I've always enjoyed playing as the Rebels. As much as I like the dominance of the Empire in terms of background, I still enjoy a challenge. To me, the rebels (ideally) are a challenge because playing them requires a cunning mentality (or at least it SHOULD). For the Rebels, it should be more than just using overwhelming force and financial security... it should require knowing the proper time and place to strike, realizing the weaknesses in the Empire's routines, annoying the heck out of the beurocracy, screwing up their logistics, etc. And I like that... it makes things more interesting for me, personally. I like having to take advantage of my enemy's weaknesses as my only means to win.
Units: Rebels... I would trade everything of the Empire (as much as I love their war stuff) for the Rebel infiltrators. Special Forces units are interesting... to me, they are the heroes of war. They are the ones that usually take the most difficult tasks, get them done, and return home in glory and fully decorated. If the Empire had a scout forces unit that was similar to the Rebel infiltrators... then this category would go to the Empire instantaneously.
Based on the Movies: Well, the first time I saw these movies was when I was three... so I was literally freaked out by the Empire! I would go with the Rebels in this category. Besides... they won! (yeah, yeah, I know that in the expanded universe there's that "remnant" thing and all that, but I'm an OT person. Strictly OT.)
Ideology: Empire by far. When it comes to sci-fi terms, I'm a human supremecist. I hate aliens, for many reasons. The main reason why I hate them is that they are so specialized that they can't do anything else other than what their race is good at. Humans, however, can do everything. And if they can't, they find a way to. We're a very inventive species... and I personally find it surprising that anybody would find another race superior to our adaptability and ingenuity. The fact that the Empire is human supremecist is enough to make me an Imperial. I also like the government structure... but I don't want to go into detail, because if I outlined why I liked the government, it would probably offend some people who live in the U.S. and like it there. (for clarification, i'm not either right or left... my views politically are sort of a mix).
Music: I would have to go with both. There's some music of the Empire (particularly in the game) that just keeps me focused... gives me a good feeling of tension and concentration. The kind of feeling that's good for a game like this, that requires thought and planning. I love tension, and the Empire's music gives me that feeling. I'm also fascinated with heroism though, and some of the themes in the Rebellion scores tend to invigorate that fascination and give me some inspiration.
As a final result... I will have to go with Empire. I'm a musician, and an idealist, so those two categories (1 empire + .5 empire compared to .5 rebel) gave the Empire the win, for my opinion.
As a side note: personal pronouns were used frequently in this post. This was to avoid making the post sound like it was fact, when it was just supposed to be opinion. It's not a rant or ramble or anything selfish, just a sharing of opinion.
There's no mystical energy field that rules my destiny