The Sidewinder followed by the Casstech Z14, both because they're integrated into the main story. With the exception of the Blade, which is Kiro's and I'm thus not comfortable captaining that while she's still around, the others are all generic ships designed to fill specific game mechanic niches and add to the lore of TiTS - both of which they do quite well, I might add, but they just don't have that personal connection the Sidewinder and Z14 do (the only ones that come close are the Aegis MS-XI, since it's used by two of the more prominent NPCs, and the Clydesdale K7, since it's a Steele Tech product).