Selenium RC, Webdriver and GRID overview

Selenium Remote Control (Selenium RC)

You should use Selenium RC, if you want to -

Run your test in different browsers on different operating systems.To write automated tests for a web application in any programming language.

What is Selenium RC?

Selenium RC is a test tool that allows the users/testers to write automated test cases/scripts in any programming language against any website using any JavaScript-enabled browser.

Selenium RC can support the following programming languages:
 Java
 C#
 PHP
 Python
 Perl
 Ruby

Advantages:

Execution is faster than Selenium IDE.
Supports multiple browsers like Google Chrome, Mozilla Firefox, Internet Explorer, etc.
Can use control and looping statements.
Supports data-driven testing.

Disadvantages:

RC disables the the javascript in the browser and injects it own while running the scripts on browsers
Execution time is slower than WebDriver.
Installing/Configuring RC is complicated than IDE.
Selenium RC Server is necessary to be running before executing the script.

Selenium WebDriver

You should use WebDriver, if you want to -

Use a particular programming language in automating/designing your test case.
Test the AJAX-based application that is rich in functionalities.
Execute tests on the HtmlUnitDriver browser.
Create customized test results.

What is WebDriver?

WebDriver is designed to address some of the limitations in the Selenium IDE and Selenium-RC like the file upload or download, pop-ups and dialogues barrier.
It drives the browser much more effectively.
It uses internal native browser javascript to drive the tests
It is a complete Object Oriented API when compared to Selenium 1.0/Selenium RC.

Advantages:

Faster Execution than Selenium IDE & Selenium RC
Communicates directly to the browser
Supports multiple browsers like Google Chrome, Mozilla Firefox, Internet Explorer, etc which
stabled or old versions
Can use control and looping statements
Supports data-driven testing

Disadvantages:

Cannot support new browsers or new browser versions
No built-in mechanism for generating test results/reports
Can't support to run the scripts on the multiple platforms

Selenium-Grid

Selenium-Grid allows us to run multiple tests at the same time on different platforms against
different browsers in parallel.
It saves time enormously when we are testing a web application.
It utilizes the hub-and-nodes concept.