What's best here, Rails Association Scopes or Just SQL?

Question

I'm not quite sure what to do here, here's the situation:

Given these models...

class Post < ActiveRecord::Base
  has_many :post_assets
  has_many :assets, :through => :post_assets

  acts_as_scopeable :assets, :scopes => [:featured]
end

class PostAssets < ActiveRecord::Base
  belongs_to :post
  belongs_to :asset

  # context is so we know the scope or role
  # the join plays
  validates_presences_of :context
end

class Asset < ActiveRecord::Base
  has_many :post_assets
  has_many :posts, :through => :post_assets
end

How do I make it so I can do something like this:

post = Post.create!(:title => "Post Title")
asset = Asset.create!(:title => "An Asset", :context => "featured")
post.assets << asset
post.reload
post.featured_assets #=> [#<Asset id: 1, title: "An Asset", created_at: "2010-06-20 16:30:51", updated_at: "2010-06-20 16:30:51">]

Assume the acts_as_scopeable method just dynamically defines the featured_assets methods (and whatever others you add).

What's confusing me is that it seems like I can do it in the following different ways:

1. acts_as_scopeable dynamically defines simple methods, and in there I do some sort of custom find on the association assets, like assets.find(:conditions => {:scope => passed_scope}}. That doesn't seem optimized though.
2. I could also define class named_scopes that do what #1 does, and then call the named scope, which just pushes of the problem.

What is the recommended way to do this, or some docs I can read to get started. Thanks!