<p>Am new to Lucene.Net
Which is the best Analyzer to use in Lucene.Net?
Also,I want to know how to use Stop words and word stemming features ?</p>

I'm also new to Lucene.Net, but I do know that the Simple Analyzer omits any stop words, and indexes all tokens/works.
Here's a link to some Lucene info, by the way, the .NET version is an almost perfect, byte-for-byte rewrite of the Java version, so the Java documentation should work fine in most cases:
http://darksleep.com/lucene/
. There's a section in there about the three analyzers, Simple, Stop, and Standard.
I'm not sure how Lucene.Net handles word stemming, but this link,
http://www.onjava.com/pub/a/onjava/2003/01/15/lucene.html?page=2
, demonstrates how to create your own Analyzer in Java, and uses a PorterStemFilter to do word-stemming.
...[T]he Porter stemming algorithm (or "Porter stemmer") is a process for removing the more common morphological and inflexional endings from words in English
I hope that is helpful.