Difference between javascript Client Object Model and SPServices ?

 Javascript Client Object Model 

If you are not limited in your project of using only OTB tools, you may use them. If you have strong requirement to use only OTB features, then use native javascript object model.

SPServices

SPServices makes work with Sharepoint more jquery-like and convenient for developers (makes many configuration work under the hood). 

SPServices is easier to use if you already know jQuery, but be carefull : the dependance of SPServices to jQuery creates sometimes some problems when jQuery is updated.

SPServices could also be a little bit longer than JCOM for querys execution. But SPServices stays a really good Framework.

Advantages features of SPService:

• It is a JQuery library.
• Supports wide range of Sharepoint Web Services.
• Works Cross Site and Cross Domain

Disadvantage:

Use old technology SOAP service which SPService wraps.Comparatively from performance perspective, COM is better as it uses JSON.