After completing both campaigns, I like the Empire better in space and the Rebellion better on the ground.
The Empire gets bigger ships earlier, and I like playing with big ships. Although the Rebellion has the best big ship of all, in the campaign you don't get it 'til the very end. With the Empire it seems like you get the Victory, quite a decent "big" ship, very soon in the tech tree based on its capabilities. It's a tech level 2 ship, whereas the slightly smaller Assault Frigate MkII is a tech level 3 ship.
And for ground assaults with the Rebellion, most of the units are more robust 1:1 compared to the Empire. I know this is why you generally get less of them, but I prefer it that way...fewer, stronger units rather than more, weaker ones.
And then you've got this
little trick on your side: Select one of your MPTL spotter drones and use his sensor ping ability to find the enemy target you're looking for (power generator, heavy factory, etc.), then once the drone has it lit up from all the way across the map, call in a bombing run. Now that's just wrong. When I discovered this I was dumbfounded. I killed the enemy's shield generator, turbo-lasers and factories before I even left the reinforcement point I landed on. Before I even hotkeyed my units into groups. Wrong, I say.
Yes, it takes a minute or two for the first bombing run to "charge up", but when I discovered this ability I was doodling around a little longer than usual right after landing. And once I discovered it, I realized it's well worth the wait for that first bombing run to become available.
What's even close to an Imperial equivalent of this? A sacrificial scout trooper? Not nearly as fast or easy. And you lose a unit in the process. And if he dies before he even gets there, or just before you can click the bombing run button, you have to do it all over again. And he has to scout around the map manually, trying to pass by lesser - although still armed and dangerous - enemy targets that can take him out. Sensor pings last a fixed amount of time and require no unit anywhere near the site of the bombing run; makes it a piece of cake.
They need to take that away. It's a huge advantage for the Alliance. "I'm gonna land, step off my transport and blow up half your sh*t before I even roll away from the reinforcement point."