I am trying to work out with ORM tool to move over to and have narrowed it down to two candidates.
nHibernate or LLBLGen Pro
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The new version of LLBLGen Pro (3.0) allows you to generate code for NHibernate, so don't have to choose :). It also allows you to split up your entities into different domains.
I still prefer the LLBLGen pro runtime though, the LINQ interpreter is more complete and it has better change tracking of fields.
Unfortunately there's not many new features in the new LLBLGen Pro 3.0 runtime, as the creator first wanted to focus more on tooling than improving the existing framework.