I have friends working in J2EE and .Net, they're both at almost expert level and doing pretty well in their company. So I think it would be just fine if you go with .net deep though personally I myself like Java.
I transferred myself from Microsoft to Java when Microsoft is still at Visual Studio 6, at that time I felt things Miscrosoft provided is always very easy to be hands on and very easy to build up something small and running, but when the appliaction is complicated and needs to be robust, it just fall apart and raise all kind of issues which made me frustrated. ... maybe now .Net technology has improved...
Java is relatively not so developer-friendly for a bigginer, but so far it works for me, it's pretty stable and fast if we make our design properly. and not much strange crash without reason ( something you're familiar when your windows crash with no reason and needs to be reboot.
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that's just my personal feeling base on my experience ...