I haven't heard of Space Brothers, which isn't surprising because I haven't been keeping up with anything going on in the anime realm. But I can give you a little bit of dirt on why Last Exile was so choppy. See, it was supposed to be about the adult characters, who are far more interesting (to me at least). But at the last minute they decided since it was anime it needed to appeal to a younger demographic, so they overlaid the whole story with the Claus & Lavie arc which... that was the most boring part of the show, and it became the main attraction. I think the show would have flowed beautifully if they'd emphasized what they intended.