What is the concensus on when to use one of these tools adversed to the other? I find Subsonic very useful in terms of getting things done quickly, but on large projects it
The advice I've gotten on the topic is that Subsonic does not scale up to handle more complex scenarios and so if you go down that road you'll end up with a job trying to swap over to a more advanced ORM.
I'm thus more interested in using NHibernate for complex cases, Castle Active Record for simpler cases and am keeping an eye on Fluent NHibernate which should make NHibernate mapping a lot easier (especially once the convention based mapping support is improved).