How should I track user activity for different tasks user has performed

I am trying to record user's activity that user performs. User is associated with 3 models for which I am trying to track his activity.

class User < ActiveRecord::Base
  has_many :tasks, :dependent => :destroy
  has_many :comments, :dependent => :destroy
  has_many :rating, :dependent => :destroy
end



class Task < ActiveRecord::Base
   belongs_to :user
end
class Rating < ActiveRecord::Base
   belongs_to :user
end
class Comment < ActiveRecord::Base
   belongs_to :user
end

1. Task model entry is created whenever user is assiged for a task.
2. Rating entry is created when other user gives a rating to that user.
3. Comment entry is created when some user comments on his task.

Now I want to list these activities of these 3 models for that user according to recency.

Should I create another table named as user_activity table and every time create a record in user_activity that table whenever any record is created in above three models. Or should I take use of above three models and search from these tables for user activity on the fly whenever user activity API is called.

What should be the best approach?