I'm not sure what you mean by a "good fleet advancement system." Personally, I was looking for a group where everyone was pretty much equal. Check out UnrepentantGaming.com if that is of interest. If you want something different, then good luck to you.
Once you go 44th, you never go back... Just sayin...
"All I ask is a tall ship and a star... to steer her by." You... You could feel the wind at your back in those days. The sounds of the sea... beneath you, and even if you take away the wind and the water... it's still the same. The ship is yours. You can feel her. And the stars are still there, Bones. ~ James T. Kirk | Imgur
As others have stated above, I'm not entirely sure what you're looking for in an advancement system.
In the Blacksheep, people with good attitudes will make their way up the ranks. Members who treat others with courtesy, are active in the game, participate and help others will likely be offered a seat on our Fleet Council given enough time. Also, a good sense of humor never hurts! Our advancement system is based on a person's attitude and how they treat others within the game.
Hope you find what you're looking for, and that you're enjoying the game!