I would call the approach in quine a lensy-mtl style. It's ok as far as it goes, but since you are using concrete environment values it isn't great if you want to do testing of things like database code without having a "real" backend hooked up. The typical approach then is to create your own type-class and instances
class MyBackend where ...
instance (MonadReader r m, HasDb r) => MyBackend m where ...
instance (MonadState s m, HasTestState s) => MyBackend m where ...
Of course, now our problem is that our module with this abstraction depends on the module with the db and the test state. Unless we create orphan instances, which I prefer to avoid. This is one area where I like the Free monad approach more because the interpreter can be built and composed with other interpreters in completely separate modules or packages because they are just values.
Rich
PS for the record, I don't strongly prefer the mtl style or the free monad style, I think they each have good qualities and bad and which one I choose tends to depend on other factors.