I am just switching from C to C# and would like to invest sometime learning database work. I am overwhelmed with the options: Linq-to-sql, ADO.NET. nHibernate, EntityFramework, plain old sql (I am used to this). Since I have only limited 'learning' hours available (about 2.5 hours per day), where should I invest my time? I don't want to learn something that will be obsolete next month or for which no one will hire me.