If your customer is paying:
You may not have to make a choice as he will possibly tell you when and where to deliver the goods. If not, be nice! Decide as though YOU were paying! And don't forget post. For small, inexpensive items, mail may be a very cheap & easy system. And if you ever need to move very big or outsize items quickly by air, don't forget charters & part charters. But beware! It's rarely as simple as it seems. For example:
A parcel of a certain weight by courier or integrator may at first glance appear to be dearer than if it were sent by consolidated airfreight. If however you take into account your customer's clearance and delivery costs at destination, the overall cost, albeit not yours, is better value - -- I leave it up to you whether this should be taken into your decision making!
Or:
Sometimes Importers will not allow integrators or couriers to clear/deliver their goods because of set arrangements already in place or VAT/Duty account issues. This can affect the way overall prices might look. If in doubt, ask!