I've developed with both WCF and straight web requests.
WCF can be great when developing web services, but there is no guarantee that all third party services will be implementing a protocol that works with WCF (add service reference or svcutil).
Also WCF has the advantage of being hosted anywhere you want, like Console, Web site, WPF application, or Windows Service. When it comes to configuration there is a high learning curve with WCF, so understand that going in.
More and more third party services are adopting a REST interface. This means most of your calls out will be done using the HttpWebRequest. Once you make the call to the service, you will have the issue of deserializing the data coming back (XML, JSON, Key/Value Pair, Fixed Length). If it is XML or JSon, look into using the XmlSerializer or DataContractSerializer.
So if you are writing your own web service (calls coming in), go ahead and use WCF. If you are consuming a web service (calling out to a service i.e. Twitter) you most likely won't have the choice to use WCF.