Is argon preferred over nitrogen for maintaining an inert atmosphere?
Speaking purely from an organic point of view, there isn't really a huge difference, labs tend to stick to one or the other, largely depending upon the availability (some universities use the boil off from the liquid nitrogen cylinders to furnish labs with nitrogen gas, whilst others have no such facilities meaning labs must buy cylinders of either nitrogen or argon). 

For serious organic groups (organometallics, total synthesis) doing a lot of air-sensitive chemistry, there can be some advantage to argon due to its higher density [argon (1.714 g/L) nitrogen (1.251 g/L)], meaning it tends to blanket the reaction, and if you need to quickly open the flask to put a reagent in then the argon doesn't escape so quickly. 

For inorganic chemists, there are situations where nitrogen will react with certain chemicals, and in these cases argon must be used.