Vasu, I think you have to be VERY careful when comparing different products. It's almost like comparing languages - it can quickly become a religious debate, so I'd prefer not to make specific comparisons between Eclipse and other products. Perhaps others would like to do that in a different thread
However, I can point out the single biggest difference between Eclipse and all the other products out there: Eclipse is an Open Source framework that was designed from the start to be extended - by people like you and me! The Eclipse designers realized that no single development team could ever meet all the needs of the entire community, so instead they designed a platform that would allow anybody with the desire to add their own features to the workbench.
Eclipse by itself actually does almost nothing. Without plug-ins, Eclipse is a very poor version of Windows Explorer. It just so happens that it ships with a really, really excellent Java plug-in, the JDT, which in most situations is every bit as powerful as VisualAge for Java (you can click here
for an article I wrote last year comparing the two, but you may have to register first).
Other plug-ins are being written every day, and that's something none of the other IDEs can say. Some of the plug-ins for Eclipse are not free. IBM's various WebSphere offerings cost money, in some cases, significant money. But they also provide levels of testing that nobody else has. And that's the thing that make Eclipse so unique. If you can get by with the free offerings, there's nothing stopping you from using Eclipse without paying a cent. At the same time, if you need advanced capabilities, there are vendors willing to sell you plug-ins that take Eclipse to that next level of function.
And that's I think the biggest difference between Eclipse and all the other IDEs.