This is a tough one to answer.
The top one right now I'd have to go with is FFG's Star War Edge of the Empire and Age of Rebellion. That is by book count on my shelf at this time. In that regard, the 2nd would be Doctor Who.
But as for style, presentation, setting, rules, and artwork- Rocket Age.
That product line is wonderful. This is one of the most solid apologetic versions of the Flash Gordon/Buck Rogers genre. Great stuff.