While booking transportation at your destination before flying is certainly a very good idea, at the same time you need to remember that a lot of the services you might look into would be quite strict about things that you have no control over. One thing you need to understand is that flying is a rather unpredictable mode of transportation. While it is certainly very safe indeed, delayed flights are a common occurrence and sometimes these delays can end up lasting a very long time indeed.
Hence, you need to avoid those shuttle services that have strict cancellation policies. A lot of services charge you the full amount or at least part of it even if your flight has been delayed, but there are a number of services out there that are a lot more lax about this. These services understand that travelling is a stressful experience for everyone and they shouldn’t add to this stress by forcing you to pay for something that you are now not going to be able to use.
A lot of services accommodate you by helping you book another car, and most of these good airport shuttle service providers offer you full refunds if your flight was cancelled and you are no longer going to be travelling to your destination.
You also need to make sure that your airport shuttle service has good drivers. Your drivers need to be polite, accommodating and above all else knowledgeable about the city that you have arrived in. The driver of your airport shuttle is going to be your first source of information upon arriving in the city, so learning from him should be something that you can do with ease and there are quite a few services that realize this.