Analysing representations History GCSE Stalin's control

Anyone who has done/is doing the Edexcel GCSE history and is doing the 20 mark controlled assessment where you have to compare three representations on Stalin in russia???

Question:
Analyse the representations and choose which one you think is best representing how Stalin's controlled the soviet union in the years 1928-39

(my school is doing it on Stalin's control and I'm finding it hard to decide how to rate the representations)

What's most important in a representation?:
accuracy
completeness
objectivity

any further advice/tips are greatly appreciated!