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