Okay, this is a simple question: Who would win in a war between the Galactic Empire of Star Wars and the Yeerk Empire in Animorphs? I think the Empire, and here are my observations to back it up. Whereas the Yeerks had only a few hundred ships, the Empire had MILLIONS of ships, including 25,000 Star Destroyers, one of which could reduce the surface of an entire inhabited planet to molten slag on its own. If we gave the Yeerks a few thousand years head start where they took over the entire galaxy, I still think that the Empire would win, at least in a straight-out fight. The Yeerks and other Animorphs species have been shown to have low numbers of ships. Worse yet, the Yeerks and the Andalites had very weak ground troops and unarmored soldiers! The Empire, on the other hand, knows that you can easily destroy a planet from orbit, but to conquer and hold a planet you need a respectable ground force, and to that end, they have speeders, AT-AT walkers, AT-ST scouts, repulsor tanks, and fully armored stormtroopers. The Yeerks might be able to destroy the surface of a planet from orbit (that is, if it wasn't shielded), but to take over planets in a straight-up fight, they would lose 99 percent of the time.
Now, here's the part of the war that gets interesting. The Yeerks' main power is their ability to infest other species. Assuming the Yeerks had taken over our galaxy, then they would naturally have Andalite hosts and their ability to create the morphing power, giving them an extra edge. I envision the Yeerks being able to slowly subjugate the Empire via infiltration, which is, quite frankly, their only way to do so. The morphing power helps in this regard. And since the Empire destroyed all the Jedi, there are no Force-sensitives for the Yeerks to infest, but I don't believe they'd be able to use Force powers even if they did infest a Force-sensitive. Then again, it goes both ways; there would be no Jedi or Sith to sense their presence in a host, although I'm pretty sure either the Emperor or Vader would be able to sense a disturbance in the Force, like they did with Luke Skywalker.
So... who would win? In infiltration, stealth, and covert tactics, the Yeerks have the Empire beat, but in raw power, sheer numbers, and ground forces, the Empire is clearly superior to the Yeerks.