With the HRE you have to think less in states, more in families.
That would be as the really big houses during the timeframe given, also the holders of the Kurfürstentitel that elected the emperor:
- House Habsburg (Bohemia)
- House Wittelsbach (Palatinate, Bavaria, Archbishopry Cologne)
- House Wettin (Saxony)
- House Hohenzollern (Brandenburg)
These families each ruled multiple smaller states as well, including the clerical states, to an extent where they basically always were the ones ruling the HRE. Habsburg fielded the emperor, Wittelsbach was always the contender, Wettin realized its ambitions through marriage and otherwise stayed out of everyone's business, Hohenzollern effectively took over the Wittelsbach role after the fall of House Wittelsbach in the late 1600s and early 1700s (when Wittelsbach took on France).
The other two Kurfürstentitel, the archbishopries of Mainz and Trier were variably held by lower-ranked families, such as Nassau, Baden, Isenburg, Metternich, von der Leyen, rarely for more than two consecutive terms.
The timeframe given (1400-1750) basically begins with the downfall of House Luxembourg in the early 1400s, giving power to the four houses above, and ends with the raising of the ninth Kurfürstentum, namely Braunschweig-Lüneburg aka Hanover in the early 1700s.