Best freestanding PHP ORM?

[Higgaion]

I'm working on a large PHP app. Porting it to a framework all in one
step is off the table. I'd like to gradually introduce good stuff,
like MVC, and the best place to start in the M. It looks like the
best freestanding PHP ORM is Doctrine? Does anyone here use it / have
a better idea? My criteria:

- Support mssql and multiple connections
- Follow the Active Record pattern
- Be dry and declarative*

* (read: as much like rails active record as passible ).