Dapper is a really awesome library when you want to write complex queries (full of table hints, output clauses, merges and other advanced stuff), but don't want to write enormous amount of code for adding parameters and reading result sets.
I've also used BLToolkit, and it is pretty fast too, plus it has Linq support to build strongly-typed queries that sometimes better than raw SQL queries. But when it comes to table hints, Linq and other stuff does not help. So, it always depends :)
