Q:

Use a WCF service or REST api for JSON?

I've just started working with SharePoint 2013 on a company that uses a WCF service to return JSON data with .svc-files and custom classes. I got the task to populate a table with items from a List, and without looking at how they did it I used jQuery and AJAX to call 
the 
http://sp/_api/web/lists/getByTitle('titlehere')/Items
to display the data. This works fine for me, but I've seen in many places that people are using the url http://sp/_vti_bin/Namespace/Service.svc/Method, as is the case with the company I'm at.
What are the differences and when should the two be used? As far as I reckon, you can use the later to manipulate the data more exclusively than when doing simple CRUD operations on the _api, even though it seem to support alot of operations.
I read on a blog that _vti_bin is older aswell. Does that mean I should focus on using the _api instead?

A:

Probably you right, I guess custom WCF service (endpoint:http://sp/_vti_bin/Namespace/Service.svc/) is used to cover specific cases that does not seem possible to perform using standard SharePoint 2013 REST API or due to performance limitations. 
But still, SharePoint 2013 REST API (_apiendpoint) should be considered  as a preferred choice for a list items manipulation.       
For example, the article Manipulating list items in SharePoint Hosted Apps using the REST API gives an explanation how to perform CRUD operations in SharePoint 2013. 

