Maybe, you just arrived in Singapore and need to reach a certain address. A professional maxicab service with GPS enabled tracking is the perfect option. Find a good site where they confirm the availability of GPS in the cars. You must be sure of paying the best rates. The site must have a phone number. Such sort of arrangements best happen over phones. Call them up and inquire whether the service can be ready at the airport on assigned time.
Your flight may be late by half an hour or more than that. You do not decide flight schedules. Check whether the company charges extra for the inadvertent waiting.
The hand at wheels
Most importantly, you need a good driver behind the wheels. Literally, passengers need to trust their lives with cab drivers. It should be unwise to neglect this obvious parameter. Make sure to ask whether the Maxi Cab taxi service employs experienced drivers. You can also ask for references, but that may not be necessary when the first interaction is convincing.
Nevertheless, you may want to talk directly with passengers who availed the cab service before. In most of the appointments, people already contact based on references from a friend. It is a good idea to reverse-check it, as that also ensures the reliability of your reference.
Other important aspects
Obviously, the cabs must have credit card processing systems. You may need to arrange cabs for visitors. When you need multiple vehicles, confirm the availability clearly with the taxi operator. If you need four cabs, make sure all of them are ready at the airport in the assigned time.
Sometimes, you need to book cabs on urgent basis. It all depends on whether a taxi is available when you need. Of course, you must check whether advanced and current bookings have the same rate or are different.