There are some concerns to develope an application.
your project scale is very important , if you wanna make an enterpise application  i generally suggest you to use J2EE Platform but for middle and small scale .Net platform has some benefits.
there are a few topics below to find  it out better :

a) learning curve of J2ee is more than .Net platfom.
b) j2ee line of codes is more than .Net
c) there are many reliabe j2ee frameworks (open source) like Struts , Hibernate , Spring , JBoss etc which can help  you make ur project well.
d)event-driven model of ASP.Net and its components help you make ur small scale project quickly.
e)...
f) Visual Studio IDE and MSDN ( good reference for development ) are valuable really .

it is better to find middleware documents for comparsion of J2ee vs .Net since 2002.