Ok I realise that this is a negative question but I also think that it would be fabulously interesting to see what everyone thinks. Note 'over-rated', not 'worst'. The ones who you hear about constantly but either can't get into or just find insipid or trite! Please also note that I have not put living composers such as John Williams, Einaudi, etc. Don't take these into consideration, I am only referring to ones who have shaped our musical past.
Please excuse any glaring omissions I have made, it is very difficult with only 20 choices (2 of which aren't composers anyway) to cover everybody's opinions of who are the 'big fish' of the composing world. And don't be afraid of being controversial! I'll start the ball rolling by voting for . . . . . . . Bach