The first thing that comes to mind about the respective high commands is Napoleon's dictum about one bad general being better than two good ones.
I can easily believe that the Federation high command, however unmarked by genius it might be, routinely has more of it's ducks in a row- more of it's shit straight if you want to put it that way- than the gaggle of backbiting, feuding prima donnas that we see far too many of in the Imperial Starfleet.
In terms of a solid, mediocre, sufficient performance, without disabling friction and destructive fratricide, point to the Federation.
Dropping them both to the same tech level, on the other hand, I am not enthused by, largely because so many of the human factors that make the Federation and the Empire what they are can be derived out of that. Think about it like this;
in the Empire, there is no outside. Not really, not that matters. Every war is a civil war, every conflict one between old neighbours. The great rationale of the modern warrior- "the true soldier fights not because he hates what is before him, but because he loves what is behind him"- simply does not apply. It's commonly said to be a different kind of personality who puts in for front line soldier and who goes for internal security. If there isn't a difference between protect and defend and chainsaw the neighbours, something's wrong. The Empire wants, and chooses, people who can kill their kin.
In the Federation, there very definitely is an outside, and it's dangerous. The core may be nigh on utopian, but further out the galaxy throws new, confusing, dangerous things at them on an unpredictable semi- routine basis. They need warrior-explorers. Some are individually happier at one and some at the other, but they do have at least some.
There is also relatively little change in the Empire. Many things may be tactically unexpected and have to be guarded against, but how many real strategic and technical surprises can there be, at the technological end of the line? Most of the ruses and tactics that can be tried have been- almost all, many times, in fact. Everyone knows all the tricks. Superior competence at them may be enough to win, but the edges of the envelope are solid. Drill and routine matter massively, flexibility- not so much. That would breed conformists, even without exploitation from above.
The Federation may have the prime directive for us to point at them and scream "hypocrite" about, but the Empire has the New Order, about which mere hypocrisy is no longer an adequate term- the depths of cynicism and corruption embodied in that are so profoundly awful, they're actually realistic. And you can bet that a lot of those involved know it. Again, there is no outside- the principles are up for sale as well.
Size isn't that much of an issue; an outpost net, an outlying sector, a small fringe segment of the Empire is easy enough to think of. I'm not sure how much the technology can stand to be changed before seriously changing the drivers that define the human factors, though.