Nick - the question of 5-string or tenor banjo is pretty basic as the two are about as similar to play as guitar is to mandoline.
If it is 5-string, you then get onto the question of what sort of music your friend actually wants to be able to play. It has a big influence on what style of banjo he/she might need to learn.
Answers to these questions, plus how far your player is capable of travelling might produce very different answers on the forum.
Quack!
GtD.