Cons: Since the toolkit is a wrapper for the SOAP API, you consume API calls for every server-side interaction.
Code Snippet (for a Visualforce use case):
Pros: Simple and very easy to use. Can be used from both within a Visualforce page and from an externally hosted web page. Since the toolkit wraps the REST API, all the advantages of using a lightweight HTTP/JSON based protocol like REST apply to this toolkit.
Cons: Similar to the AJAX toolkit, you consume API calls when using ForceTK. The REST API does not support bulk DML operations and by extension, neither does ForceTK.
Pros: Unlike ForceTK, you don’t consume any API calls when using the RemoteTK library.
Cons: Unlike ForceTK which only requires a simple import of the forcetk.js library, this option requires you to add an Apex Class and Component to your Org. This library also cannot be used from outside the Force.com Platform.
Pros: Ability to build a Force.com web/mobile application using a modern MVC framework like Backbone.js.
Cons: Requires knowledge of Backbone.js (which really isn’t a con!)
Pros: Very easy to setup and use. Supports both the REST and Streaming API. Built-in support for session handling with express middleware.
Cons: Requires knowledge of Node.js (again, not a con!)