I think it would be best not to do something someone else has suggested for you to do.
The best idea is to do something you'll enjoy researching. If you enjoy ancient history start there; decide what sort of history you like e.g military history, personalities, societies etc and go from there.
i was having difficultly deciding what i wanted to do so i looked at what i like in history. I like ancient history,looking at personalities from the past and roman society, so i focused my assignment on an ancient roman personality.
if you do something you like and show good historical research markers will like to read your assignment. It doesnt have to be on a subject that they really enjoy because if they mark it hard because they dont fancy the topic they aren't marking properly.