You should always use a maximum diameter needles to achieve a compaction over larger areas for single point insertion.
The size of the needle is dependent of the clear space available for insertion, say if i have congested reinforcement bars i can not insert 80 mm size needle in column during concreting when the clear space is say 80 or 60 mm.
Higher size needles increases the compaction efforts thus the productivity is improved.
Small size does has smaller area in radius of its insertion point into concrete to make compaction efforts, so it need to be inserted at more close interval to achieve right amount of compaction.