Well, my Primary Modeling Preferences are:
-> 1/72 scale Armor and Aircraft
-> 1/600 scale Ships.
However, I build just about any scale commercial ship as long as it looks good. When it's a warship, I get specific:
-> Cruisers, destroyers, submarines, light fleet carriers, patrol boats and 'phibs in 1/700 scale.
-> Battleships and full-sized carriers in 1/500 to 1/600 scale.
I also build all eras too, I have no primary preference there.
My other primary preferences in Sci-Fi are anything from favorite TV shows or movies.
Preference for Cars, anything from Tom Daniel's, the 1930's or older, including European designs. Followed by show cars from TV and the movies, and the '57 Chevy.