Familiars aren't actually categorized in the same way shifter forms are, but yes they are certainly balanced in various ways. Like Homard said, some of them excel in combat while others have special abilities in the form of skills or detects that help the conjurer.

Some folks prefer a heartier "tank" familiar while others are happy with a relatively fragile one that does nothing more than provide passive bonuses or scouting ability. And like shifters, you don't get to pick which one you get, exactly.