An interesting question came on SharePoint StackExchange: How to retrieve the guid of the last uploaded file. It is only possible in CSOM as far as I know. But if we simplify the task, how to get the id of the last item, the we can compare three ways of getting them: SPServices, jQuery + listdata.svc and CSOM.

SPServices

The most easiest way, but not available in async:

$().SPServices.SPGetLastItemId({	
	listName: "Documents"
});

listdata.svc

Just combine some query strings and try in the browsers address bar:

Referencing javascript libraries from Content Delivery Networks (CDN) like jQuery can have many benefits. The self-hosted javascript files are on the other hand give you more control. But in one situation it is much better with cdns: the development. Like Marc D Anderson pointed:

I didn’t realize it at the time, but this txt file has become a standard part of my toolkit already. I’ve added it to three client environments just since last week. It’s the A #1 fastest way to get something up and running, even if you know you’re going to host the files locally later.

SPServices is a great tool, really nice work, Marc Anderson (@sympmarc). It has been there all the time I have developed for SharePoint. But the fact that you work with XML and you must parse the attributes (!) was the reason why I prefered listdata.svc and Client Object Model, where you get objects in JSON or you have a nice API to get objects and their properties. But there is an area where SPServices are really the best tool: SharePoint Web Services which only understand SOAP like SocialDataService.asmx.