Most ORMs have their own strengths and weaknesses.
Entity Framework, for example, has the (huge?) advantage of being in the framework itself, but it also is fairly heavy-weight, and a bit more difficult to get up and running (steeper learning curve).
There are some very nice, very easy to use commercial ORMs. I'm currently using Lightspeed in a C# 4 project, and extremely happy with it for this specific scenario.
It really comes down to what you need from the ORM. If you want very quick and easy to setup and use, Lightspeed, subsonic, and others are very nice. If you need full featured, then Entity Framework and NHibernate are good options.
