Server / client - what kind of solution should I use?

Question

My Current Situation: I got many instances of same application that read XML files from shared folder. that makes many calls to read file and sometimes locking the files.. What I look for: I want to move to Server / Client solution. I want to reduce the calls to the disk. I want the server app to keep read the data from the files once per interval. and store only the required data in objects. Client: ask for the data from the server. so, what do you think should I use? WCF / WebService? some ideas please.