Picking an ORM tool - So many choices, and so little time

After much reading, playing and fiddling, I am still not sure what ORM tool is the one i should be using above others.I am usign the Dotnet stack.

I have looked at:

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• Entity framework
• LLBLgen Pro
• NHibernate

Currenlty I am rather impressed with LLBLGen Pro.

I have also read about Castle's active record, sub sonic and Linq to SQL.

Why should i use one over the other and what are the pitfalls of using this one over that one?

How should i try and make the informed desicion.

I am concerened about some large gotcha that i might not see at this stage that will only come to life far into the development cycle and then have cause major hassles.

Thanks for all the help.

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I have used both NHibernate and Entity Framework and both are great. If you like a more drag-and-drop approach, entity framework is the best choice and maybe the easiest to get started with. If you need a ORM for a commercial product maybe it's easier to sell EF (because Microsoft is behind it). At least that is my experience. But, I'm using HNibernate at my current project (at a customer) and we are very pleased with it. It has a bit of a learning curve, but once you get the hang of it it's pretty productive to use. The only drawback is the XML hacking you have to do. If you have the possibility to use EF 4 I think that would be my recommendation. If not, go for NHibernate.