<p>I am using C# 3.0 / .NET 3.5 and planning to build an eCommerce website.</p>

<p>I've seen NHibernate, LLBLGEN, Genome, Linq to SQL, Entity Framework, SubSonic, etc.</p>

<p>I don't want to code everything by hand. If there is some specific bottleneck I'll manage to optimize the database/code.</p>

<p>Which ORM would be best? There is so much available those day that I don't even know where to start. </p>

<p>Which feature(s) should I be using?</p>

<p>Links, Screencast and Documentation are welcome.</p>

I can only really speak for LINQ-SQL and can say that it is:
Easy to use
Quick to get you up and running
Good for simple schemas and object models
but it starts to fall down if:
You're using a disconnected (tiered) architecture because its datacontexts require the same object instances to perform tracking and concurrency (though there are ways around this).
You have a complex object model / database
Plus it has some other niggles and strange behaviour
I'm looking to try EF next myself and MS seem to be quietly dropping LINQ-SQL in favour of EF, which isn't exactly a ringing recommendation of LINQ-SQL :)