Different ways of accessing SharePoint list.

TYPE OF SERVICE/API	WHEN TO USE
Server-side object model	Core SharePoint DLL that is used for building  applications that aredeployed to or reside (or consumed) on the server.
Client object model	Client-based DLL used for coding against SharePoint on remote clients. It is supported in .NET, Silverlight, and JavaScript applications.
WCF Data	Services REST-based service that provides lightweight GET and POST functionality against a SharePoint list. You use this service to interact with Excel spreadsheets. (Note that the WCF Data Services were formerly called ADO.NET Data Services.)