I love Java more about numerous reliable open  source frameworks  , but .Net is young .
I Love Java more about platform-independency in a broad range of Computers ( from Mobiles to Mainframes ) and Operation Systems (from Symbian to OS/390) against the current versions of .Net CLR. [Rotor , Mono , Portable.Net are not for commercial usage]
I Love Java for nice architecture and specification of EJB Technology against the Enterprise services  ( COM+ , Not Redistributable) in .Net Technology.
But I Love to .Net for Simplicity and Speed.
I love .Net for Attribute keywrod and attributes usage.

fo some reasons and usage .Net is better and for some other reasons and usage Java s better . but in an abstract view Java is better than .Net.
however i suggest to study some eBooks .
J2EE and .NET Application Server and web  Services Benchmark
Middleware Company
October 2002
J2EE and .NET (RELOADED)
Yet Another Performance Case Study
The Middleware Company Case Study Team
June 2003
The Comparison of J2EE and .NET for e-Business
The Technical Report (hipic-10292003) of High-performance Information
Computing Center at California State University, Los Angeles
2003
J2EE vs. Microsoft.NET
A comparison of building XML-based web services
By Chad Vawter and Ed Roman
June 2001