The short answer is that it depends on how much you drive and what the manufacturer says. Both kinds of service exist because cars wear in different ways depending on how they are used.
Start with the handbook
Your car's service book or handbook sets out when each service is due, by time and by mileage. Newer cars often alternate between smaller and larger services on a fixed schedule. Follow that schedule, because it is what the manufacturer designed the car to need.
When an interim service makes sense
You drive a high mileage, so a full service interval comes round in well under a year.
Most of your journeys are short, or you drive in a lot of stop-start traffic, which is harder on oil and brakes.
The car is older and you want an extra check between full services.
When a full service is the better choice
It has been a year or more since the last service.
You are coming up to a mileage the handbook marks as a major service.
You are about to buy or sell the car and want a clear record of its condition.
Not sure?
Tell us the make, model and mileage when you book online and add a note if you are unsure. The services page shows how long each service takes and what it costs.