The Size and Weight of the goods.
You heard that sea freight services are cheaper than air freight services. It may be true for per container load. However, if your shipments are less than a container load, the prices are charged by the cubic meter or weight whichever is higher. At the same time, warehousing fees at ports are way more costly than that of airports. Thus it is best to choose air freight delivery if your goods are lighter and smaller. Ask the seller to pack into lighter and smaller size will be a better choice.
Need the Items urgently.
Of course, Air freight is faster than sea freight.
Sensitive Item.
Sensitive item will be charge >2X higher than normal items. In this case, you may want to use sea freight.
Time Sensitive.
Air freight is a time sensitive mode of transport, airlines tend to be more punctual on their flight schedules. There is a wide range of daily flights to and fro major cities around the world. Ocean freight forwarder, on the other hand, is often off-schedule due to environment/weather issues.