STI vs Delegation

Hi,

This is my recent project where is started to use STI for extend my Ad
model. I never before used STI and many people which i recently discuss
not recommended me to use this method.

1. What are the advantages and disadvanteges of STI and why i should use
delegation ??

2. And how in delegation i can separate validation like below?

Ride coordination board: Singe Table Inheritance
Database: ads
  :title
  :price
  :content
  :username
  :from
  :to
Model: regular AD
  :title
  :price
  :ad_content
  :username
Model: Ride AD
  :title
  :price
  :username