Which .NET ORM has best support for PostgreSQL database

I haven't compared it against DbLinq but LlbgenPro supports Postgres and is very strong. It supports both Linq and generating the model from the database. In it's just released v3.0 it can generate projects not just for the LlblGen runtime but also for NHibernate, Entity Framework and LinqToSql.

It should be in your list to evaluate.

I would say NHibernate is your friend here.

Quite an old question, but for anyone happening upon this now (like me), please do check out the Marten document & event store for PostgreSQL/.net